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/imx8mm_venice_defconfig b/configs/imx8mm_venice_defconfig
index d5a2015..9586f65 100644
--- a/configs/imx8mm_venice_defconfig
+++ b/configs/imx8mm_venice_defconfig
@@ -31,6 +31,7 @@
 CONFIG_USE_PREBOOT=y
 CONFIG_PREBOOT="gsc wd-disable"
 CONFIG_BOARD_LATE_INIT=y
+CONFIG_SPL_MAX_SIZE=0x25000
 CONFIG_SYS_MMCSD_RAW_MODE_U_BOOT_USE_SECTOR=y
 CONFIG_SYS_MMCSD_RAW_MODE_U_BOOT_SECTOR=0x300
 CONFIG_SPL_I2C=y