Convert CONFIG_SPL_PAD_TO et al to Kconfig

This converts the following to Kconfig:
   CONFIG_SPL_PAD_TO
   CONFIG_SPL_MAX_SIZE
   CONFIG_TPL_PAD_TO
   CONFIG_TPL_MAX_SIZE

Note that we need to make TPL_MAX_SIZE be hex, and so move and convert the
existing places.

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/P2020RDB-PC_36BIT_SPIFLASH_defconfig b/configs/P2020RDB-PC_36BIT_SPIFLASH_defconfig
index a99f46a..7e9c54b 100644
--- a/configs/P2020RDB-PC_36BIT_SPIFLASH_defconfig
+++ b/configs/P2020RDB-PC_36BIT_SPIFLASH_defconfig
@@ -31,6 +31,7 @@
 CONFIG_BOARD_EARLY_INIT_R=y
 # CONFIG_MISC_INIT_R is not set
 # CONFIG_SPL_FRAMEWORK is not set
+CONFIG_SPL_MAX_SIZE=0x20000
 CONFIG_SPL_SPI_BOOT=y
 CONFIG_SPL_FLUSH_IMAGE=y
 CONFIG_SPL_ENV_SUPPORT=y