MX51: removed warnings for the mx51evk

The patch removes warnings at compile time and provides
some cleanup code:
- Removed comment on NAND (not yet supported) from lowlevel_init.S
- Removed NFMS bit definition from imx-regs.h
  The bit is only related to MX.25/35 and can lead to confusion
- Moved is_soc_rev() to soc specific code (removed from mx51evk.c)

Signed-off-by: Stefano Babic <sbabic@denx.de>
diff --git a/board/freescale/mx51evk/mx51evk.c b/board/freescale/mx51evk/mx51evk.c
index df0e8ed..af1b0bd 100644
--- a/board/freescale/mx51evk/mx51evk.c
+++ b/board/freescale/mx51evk/mx51evk.c
@@ -26,6 +26,7 @@
 #include <asm/arch/mx51_pins.h>
 #include <asm/arch/iomux.h>
 #include <asm/errno.h>
+#include <asm/arch/sys_proto.h>
 #include <i2c.h>
 #include <mmc.h>
 #include <fsl_esdhc.h>
@@ -48,16 +49,6 @@
 	return system_rev;
 }
 
-static inline void set_board_rev(int rev)
-{
-	system_rev |= (rev & 0xF) << 8;
-}
-
-inline int is_soc_rev(int rev)
-{
-	return (system_rev & 0xFF) - rev;
-}
-
 int dram_init(void)
 {
 	gd->bd->bi_dram[0].start = PHYS_SDRAM_1;