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/pico-imx7d_bl33_defconfig b/configs/pico-imx7d_bl33_defconfig
index 18fa002..d814a42 100644
--- a/configs/pico-imx7d_bl33_defconfig
+++ b/configs/pico-imx7d_bl33_defconfig
@@ -26,6 +26,7 @@
 CONFIG_FIT_VERBOSE=y
 CONFIG_USE_BOOTCOMMAND=y
 CONFIG_BOOTCOMMAND="run distro_bootcmd"
+CONFIG_SPL_MAX_SIZE=0xe000
 CONFIG_SPL_I2C=y
 CONFIG_SPL_USB_HOST=y
 CONFIG_SPL_USB_GADGET=y