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/firefly-rk3288_defconfig b/configs/firefly-rk3288_defconfig
index c0dbd84..629272a 100644
--- a/configs/firefly-rk3288_defconfig
+++ b/configs/firefly-rk3288_defconfig
@@ -20,6 +20,7 @@
 CONFIG_DEFAULT_FDT_FILE="rk3288-firefly.dtb"
 CONFIG_SILENT_CONSOLE=y
 CONFIG_DISPLAY_BOARDINFO_LATE=y
+CONFIG_SPL_PAD_TO=0x7f8000
 CONFIG_SPL_STACK_R=y
 CONFIG_SPL_STACK_R_MALLOC_SIMPLE_LEN=0x2000
 CONFIG_CMD_GPIO=y