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/stm32f746-disco_spl_defconfig b/configs/stm32f746-disco_spl_defconfig
index 440022d..1eeae3a 100644
--- a/configs/stm32f746-disco_spl_defconfig
+++ b/configs/stm32f746-disco_spl_defconfig
@@ -26,6 +26,7 @@
 CONFIG_BOOTARGS="console=ttyS0,115200 earlyprintk consoleblank=0 ignore_loglevel"
 # CONFIG_DISPLAY_CPUINFO is not set
 CONFIG_BOARD_LATE_INIT=y
+CONFIG_SPL_PAD_TO=0x8000
 CONFIG_SPL_BOARD_INIT=y
 CONFIG_SPL_SYS_MALLOC_SIMPLE=y
 CONFIG_SPL_MTD_SUPPORT=y