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/am43xx_evm_usbhost_boot_defconfig b/configs/am43xx_evm_usbhost_boot_defconfig
index 2bd98cf..14a3450 100644
--- a/configs/am43xx_evm_usbhost_boot_defconfig
+++ b/configs/am43xx_evm_usbhost_boot_defconfig
@@ -14,6 +14,7 @@
 CONFIG_BOOTCOMMAND="run findfdt; run finduuid; run distro_bootcmd"
 CONFIG_SYS_CONSOLE_INFO_QUIET=y
 # CONFIG_MISC_INIT_R is not set
+CONFIG_SPL_MAX_SIZE=0x37690
 CONFIG_SPL_FS_LOAD_PAYLOAD_NAME="u-boot.img"
 CONFIG_SPL_MTD_SUPPORT=y
 CONFIG_SPL_NAND_DRIVERS=y