config: Use CONFIG_SYS_BIG_ENDIAN in code whenever possible

So CONFIG_SYS_BIG_ENDIAN is our cross architecture option for
selecting machine endian, while the old CONFIG_CPU_BIG_ENDIAN
is defined by Arc only.

Use it whenever possible to ensure big endian code path is enabled
for all possible big endian machines.

Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
diff --git a/drivers/mtd/nand/raw/brcmnand/brcmnand.c b/drivers/mtd/nand/raw/brcmnand/brcmnand.c
index b7bf7cc..b1af3f7 100644
--- a/drivers/mtd/nand/raw/brcmnand/brcmnand.c
+++ b/drivers/mtd/nand/raw/brcmnand/brcmnand.c
@@ -1698,7 +1698,7 @@
 	desc->cmd_irq = (dma_cmd << 24) |
 		(end ? (0x03 << 8) : 0) | /* IRQ | STOP */
 		(!!begin) | ((!!end) << 1); /* head, tail */
-#ifdef CONFIG_CPU_BIG_ENDIAN
+#ifdef CONFIG_SYS_BIG_ENDIAN
 	desc->cmd_irq |= 0x01 << 12;
 #endif
 	desc->dram_addr = lower_32_bits(buf);