serial: arm_dcc: Use CONFIG_ARM64 not CONFIG_CPU_ARMV8

The only place we use CONFIG_CPU_ARMV8 was in the arm_dcc serial driver.
Switch this to CONFIG_ARM64 today, and if in the future we need finer
granularity tuning here, a new CONFIG_SERIAL option needs to be
introduced.

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/drivers/serial/arm_dcc.c b/drivers/serial/arm_dcc.c
index dfcb6fd..a402a12 100644
--- a/drivers/serial/arm_dcc.c
+++ b/drivers/serial/arm_dcc.c
@@ -51,7 +51,7 @@
 #define status_dcc(x)	\
 		__asm__ volatile ("mrc p14, 0, %0, c14, c0, 0\n" : "=r" (x))
 
-#elif defined(CONFIG_CPU_ARMV8)
+#elif defined(CONFIG_ARM64)
 /*
  * ARMV8
  */