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/sama5d4ek_spiflash_defconfig b/configs/sama5d4ek_spiflash_defconfig
index 4690406..364e949 100644
--- a/configs/sama5d4ek_spiflash_defconfig
+++ b/configs/sama5d4ek_spiflash_defconfig
@@ -34,6 +34,7 @@
 CONFIG_USE_BOOTCOMMAND=y
 CONFIG_BOOTCOMMAND="sf probe 0; sf read 0x21000000 0x60000 0xc000; sf read 0x22000000 0x6c000 0x394000; bootz 0x22000000 - 0x21000000"
 # CONFIG_DISPLAY_BOARDINFO is not set
+CONFIG_SPL_MAX_SIZE=0x18000
 CONFIG_SPL_DM_SPI_FLASH=y
 CONFIG_SPL_SPI_LOAD=y
 CONFIG_SYS_SPI_U_BOOT_OFFS=0x10000