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/mt7620_rfb_defconfig b/configs/mt7620_rfb_defconfig
index 8a4124e..048a83c 100644
--- a/configs/mt7620_rfb_defconfig
+++ b/configs/mt7620_rfb_defconfig
@@ -23,6 +23,7 @@
 CONFIG_FIT=y
 # CONFIG_ARCH_FIXUP_FDT_MEMORY is not set
 CONFIG_SYS_MALLOC_BOOTPARAMS=y
+CONFIG_SPL_MAX_SIZE=0x10000
 CONFIG_SPL_SYS_MALLOC_SIMPLE=y
 CONFIG_SPL_NOR_SUPPORT=y
 # CONFIG_CMD_ELF is not set