serial: Rename SERIAL_SUPPORT to SERIAL

Rename these options so that CONFIG_IS_ENABLED can be used with them.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/arm/mach-at91/spl_at91.c b/arch/arm/mach-at91/spl_at91.c
index d0c7325..ea19ec3 100644
--- a/arch/arm/mach-at91/spl_at91.c
+++ b/arch/arm/mach-at91/spl_at91.c
@@ -136,7 +136,7 @@
 	at91_periph_clk_enable(ATMEL_ID_PIOC);
 #endif
 
-#if defined(CONFIG_SPL_SERIAL_SUPPORT)
+#if defined(CONFIG_SPL_SERIAL)
 	/* init console */
 	at91_seriald_hw_init();
 	preloader_console_init();