arm: am437x: cm-t43: migrate CONFIG_DM_SERIAL to config file

Move CONFIG_DM_SERIAL to cm_t43_defconfig. This forces us to update the
CONFIG_SYS_NS16550_REG_SIZE value for SPL.

Cc: Tom Rini <trini@konsulko.com>
Cc: Albert Aribaud <albert.u.boot@aribaud.net>
Cc: Igor Grinberg <grinberg@compulab.co.il>
Signed-off-by: Nikita Kiryanov <nikita@compulab.co.il>
Reviewed-by: Tom Rini <trini@konsulko.com>

configs/cm_t43_defconfig

@@ -10,3 +10,4 @@ CONFIG_CMD_GPIO=y
 # CONFIG_CMD_NFS is not set
 CONFIG_DM=y
 CONFIG_SYS_NS16550=y
+CONFIG_DM_SERIAL=y

include/configs/cm_t43.h

@@ -18,10 +18,12 @@
 #include <asm/arch/omap.h>
 
 /* Serial support */
-#define CONFIG_DM_SERIAL
 #define CONFIG_SYS_NS16550_SERIAL
 #define CONFIG_SYS_NS16550_CLK		48000000
 #define CONFIG_SYS_NS16550_COM1		0x44e09000
+#ifdef CONFIG_SPL_BUILD
+#define CONFIG_SYS_NS16550_REG_SIZE	(-4)
+#endif
 
 /* NAND support */
 #define CONFIG_NAND