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/am57xx_evm_defconfig b/configs/am57xx_evm_defconfig
index 2769d35..400a1ae 100644
--- a/configs/am57xx_evm_defconfig
+++ b/configs/am57xx_evm_defconfig
@@ -26,6 +26,7 @@
 # CONFIG_MISC_INIT_R is not set
 CONFIG_AVB_VERIFY=y
 CONFIG_ANDROID_AB=y
+CONFIG_SPL_MAX_SIZE=0x7bc00
 CONFIG_SPL_SYS_MALLOC_SIMPLE=y
 CONFIG_SPL_DMA=y
 CONFIG_SPL_FS_LOAD_PAYLOAD_NAME="u-boot.img"