mx6: ddr: Allow changing REFSEL and REFR fields

Currently MX6 SPL DDR initialization hardcodes the REF_SEL and
REFR fields of the MDREF register as 1 and 7, respectively for
DDR3 and 0 and 3 for LPDDR2.

Looking at the MDREF initialization done via DCD we see that
boards do need to initialize these fields differently:

$ git grep 0x021b0020 board/
board/bachmann/ot1200/mx6q_4x_mt41j128.cfg:DATA 4 0x021b0020 0x00005800
board/ccv/xpress/imximage.cfg:DATA 4 0x021b0020 0x00000800 /* MMDC0_MDREF */
board/freescale/mx6qarm2/imximage.cfg:DATA 4 0x021b0020 0x7800
board/freescale/mx6qarm2/imximage.cfg:DATA 4 0x021b0020 0x00005800
board/freescale/mx6qarm2/imximage_mx6dl.cfg:DATA 4 0x021b0020 0x00005800
board/freescale/mx6qarm2/imximage_mx6dl.cfg:DATA 4 0x021b0020 0x00005800
board/freescale/mx6qsabreauto/imximage.cfg:DATA 4 0x021b0020 0x00005800
board/freescale/mx6qsabreauto/mx6dl.cfg:DATA 4 0x021b0020 0x00005800
board/freescale/mx6qsabreauto/mx6qp.cfg:DATA 4 0x021b0020 0x00005800
board/freescale/mx6sabresd/mx6dlsabresd.cfg:DATA 4      0x021b0020 0x00005800
board/freescale/mx6sabresd/mx6q_4x_mt41j128.cfg:DATA 4 0x021b0020 0x00005800
board/freescale/mx6slevk/imximage.cfg:DATA 4 0x021b0020 0x00001800
board/freescale/mx6sxsabreauto/imximage.cfg:DATA 4 0x021b0020 0x00000800
board/freescale/mx6sxsabresd/imximage.cfg:DATA 4 0x021b0020 0x00000800
board/warp/imximage.cfg:DATA 4 0x021b0020 0x00001800

So introduce a mechanism for users to be able to configure
REFSEL and REFR fields as needed.

Keep all the mx6 SPL users in their current REF_SEL and REFR values,
so no functional changes for the existing users.

Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Reviewed-by: Eric Nelson <eric@nelint.com>
diff --git a/board/barco/platinum/spl_picon.c b/board/barco/platinum/spl_picon.c
index 098542f..ec57cf1 100644
--- a/board/barco/platinum/spl_picon.c
+++ b/board/barco/platinum/spl_picon.c
@@ -138,6 +138,8 @@
 		.sde_to_rst = 0x10,	/* 14 cycles, 200us (JEDEC default) */
 		.rst_to_cke = 0x23,	/* 33 cycles, 500us (JEDEC default) */
 		.ddr_type = DDR_TYPE_DDR3,
+		.refsel = 1,	/* Refresh cycles at 32KHz */
+		.refr = 7, 	/* 8 refresh commands per refresh cycle */
 	};
 
 	mx6sdl_dram_iocfg(width, &mx6sdl_ddr_ioregs, &mx6sdl_grp_ioregs);
diff --git a/board/barco/platinum/spl_titanium.c b/board/barco/platinum/spl_titanium.c
index a3a4255..d1ba85a 100644
--- a/board/barco/platinum/spl_titanium.c
+++ b/board/barco/platinum/spl_titanium.c
@@ -141,6 +141,8 @@
 		.sde_to_rst = 0x10,	/* 14 cycles, 200us (JEDEC default) */
 		.rst_to_cke = 0x23,	/* 33 cycles, 500us (JEDEC default) */
 		.ddr_type = DDR_TYPE_DDR3,
+		.refsel = 1,		/* Refresh cycles at 32KHz */
+		.refr = 7,		/* 8 refresh commands per refresh cycle */
 	};
 
 	mx6dq_dram_iocfg(width, &mx6dq_ddr_ioregs, &mx6dq_grp_ioregs);