include: Use more consistent name for atomic xchg() and cmpxchg()

We should remove the "arch_" prefix from atomic xchg() and cmpxchg()
function names to have consistent naming of all atomic functions.

Signed-off-by: Anup Patel <anup.patel@wdc.com>
Reviewed-by: Atish Patra <atish.patra@wdc.com>

lib/sbi/sbi_init.c

@@ -285,7 +285,7 @@ void __noreturn sbi_init(struct sbi_scratch *scratch)
 	    sbi_platform_hart_invalid(plat, hartid))
 		sbi_hart_hang();
 
-	if (arch_atomic_xchg(&coldboot_lottery, 1) == 0)
+	if (atomic_xchg(&coldboot_lottery, 1) == 0)
 		coldboot = TRUE;
 
 	if (coldboot)