arm: imx6q: pcm058: Rework SPI NOR configuration

Enable CONFIG_SPL_DM_SPI_FLASH to be able to boot from SPI NOR,
modify the offset of U-boot proper in the SPI NOR, so the
difference in offset matches between SPL and U-boot matches that of
the SD Card, allowing u-boot-with-spl.imx to also be copied to SPI
NOR at an offset of 0x400. Update the README to reflect this
change.

Signed-off-by: Niel Fourie <lusus@denx.de>
Cc: Stefano Babic <sbabic@denx.de>
diff --git a/configs/pcm058_defconfig b/configs/pcm058_defconfig
index c491cbf..b085a7d 100644
--- a/configs/pcm058_defconfig
+++ b/configs/pcm058_defconfig
@@ -7,7 +7,7 @@
 CONFIG_ENV_SIZE=0x4000
 CONFIG_ENV_OFFSET=0x100000
 CONFIG_ENV_SECT_SIZE=0x10000
-CONFIG_SYS_SPI_U_BOOT_OFFS=0x40000
+CONFIG_SYS_SPI_U_BOOT_OFFS=0x31400
 CONFIG_MX6_OCRAM_256KB=y
 CONFIG_TARGET_PCM058=y
 CONFIG_SPL_TEXT_BASE=0x00908000
@@ -34,6 +34,7 @@
 CONFIG_SYS_MMCSD_RAW_MODE_U_BOOT_SECTOR=0x18a
 CONFIG_SPL_DMA=y
 CONFIG_SPL_FS_EXT4=y
+CONFIG_SPL_DM_SPI_FLASH=y
 CONFIG_SPL_SPI_LOAD=y
 CONFIG_SPL_WATCHDOG_SUPPORT=y
 CONFIG_SPL_YMODEM_SUPPORT=y