serial: Convert ARM_DCC to Kconfig

The symbol "CONFIG_ARM_DCC" is used to control building
drivers/serial/arm_dcc.c.  Provide a simple Kconfig entry for this.

Cc: Luca Ceresoli <luca@lucaceresoli.net>
Cc: Michal Simek <monstr@monstr.eu>
Cc: Tom McLeod <tom.mcleod@opalkelly.com>
Cc: Mike Looijmans <mike.looijmans@topic.nl>
Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Luca Ceresoli <luca@lucaceresoli.net>
diff --git a/configs/bitmain_antminer_s9_defconfig b/configs/bitmain_antminer_s9_defconfig
index 9f88023..ef5f567 100644
--- a/configs/bitmain_antminer_s9_defconfig
+++ b/configs/bitmain_antminer_s9_defconfig
@@ -66,6 +66,7 @@
 CONFIG_ZYNQ_GEM=y
 CONFIG_DEBUG_UART_ZYNQ=y
 CONFIG_DEBUG_UART_ANNOUNCE=y
+CONFIG_ARM_DCC=y
 CONFIG_ZYNQ_SERIAL=y
 # CONFIG_WATCHDOG is not set
 CONFIG_WDT=y