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/imx8mn_beacon_defconfig b/configs/imx8mn_beacon_defconfig
index d2d182d..865b06b 100644
--- a/configs/imx8mn_beacon_defconfig
+++ b/configs/imx8mn_beacon_defconfig
@@ -31,6 +31,7 @@
 CONFIG_BOOTCOMMAND="mmc dev ${mmcdev}; if mmc rescan; then if run loadbootscript; then run bootscript; else if run loadimage; then run mmcboot; else run netboot; fi; fi; else booti ${loadaddr} - ${fdt_addr}; fi"
 CONFIG_DEFAULT_FDT_FILE="imx8mn-beacon-kit.dtb"
 CONFIG_ARCH_MISC_INIT=y
+CONFIG_SPL_MAX_SIZE=0x25000
 CONFIG_SPL_BOARD_INIT=y
 CONFIG_SPL_BOOTROM_SUPPORT=y
 CONFIG_SYS_MMCSD_RAW_MODE_U_BOOT_USE_SECTOR=y