Convert CONFIG_SPL_SERIAL_SUPPORT to Kconfig

Move this option to Kconfig and tidy up existing uses.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/P1022DS_36BIT_NAND_defconfig b/configs/P1022DS_36BIT_NAND_defconfig
index 780da26..3d63c8e 100644
--- a/configs/P1022DS_36BIT_NAND_defconfig
+++ b/configs/P1022DS_36BIT_NAND_defconfig
@@ -1,4 +1,6 @@
 CONFIG_PPC=y
+CONFIG_SPL_NAND_SUPPORT=y
+CONFIG_SPL_SERIAL_SUPPORT=y
 CONFIG_MPC85xx=y
 CONFIG_TARGET_P1022DS=y
 CONFIG_PHYS_64BIT=y
@@ -9,13 +11,13 @@
 CONFIG_SYS_EXTRA_OPTIONS="NAND"
 CONFIG_BOOTDELAY=10
 CONFIG_SPL=y
-CONFIG_SPL_NAND_SUPPORT=y
 CONFIG_TPL=y
 CONFIG_TPL_ENV_SUPPORT=y
 CONFIG_TPL_I2C_SUPPORT=y
 CONFIG_TPL_LIBCOMMON_SUPPORT=y
 CONFIG_TPL_LIBGENERIC_SUPPORT=y
 CONFIG_TPL_MPC8XXX_INIT_DDR_SUPPORT=y
+CONFIG_TPL_SERIAL_SUPPORT=y
 CONFIG_HUSH_PARSER=y
 CONFIG_CMD_MMC=y
 CONFIG_CMD_SF=y