ppc/85xx: Make flash TLB entry determined at runtime on FSL boards

Rather than hard coding which TLB entry the FLASH is mapped with we can
use find_tlb_idx to determine the entry.

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>
diff --git a/board/freescale/mpc8572ds/mpc8572ds.c b/board/freescale/mpc8572ds/mpc8572ds.c
index 556846a..64e164b 100644
--- a/board/freescale/mpc8572ds/mpc8572ds.c
+++ b/board/freescale/mpc8572ds/mpc8572ds.c
@@ -264,7 +264,7 @@
 int board_early_init_r(void)
 {
 	const unsigned int flashbase = CONFIG_SYS_FLASH_BASE;
-	const u8 flash_esel = 2;
+	const u8 flash_esel = find_tlb_idx((void *)flashbase, 1);
 
 	/*
 	 * Remap Boot flash + PROMJET region to caching-inhibited