powerpc/85xx: provide 85xx flush_icache for cmd_cache

This provides a function that will override the weak function
flush_icache to let 85xx boards to flush the icache

cc: Kumar Gala <kumar.gala@freescale.com>
Signed-off-by: Matthew McClintock <msm@freescale.com>

arch/powerpc/cpu/mpc85xx/start.S

@@ -676,6 +676,8 @@ mck_return:
 
 /* Cache functions.
 */
+.globl flush_icache
+flush_icache:
 .globl invalidate_icache
 invalidate_icache:
 	mfspr	r0,L1CSR1