u-boot.mk: add support for config customization
Make it possible to easily customize U-Boot config options via new
`UBOOT_CUSTOMIZE_CONFIG` variable, so we don't need to patch config
files or override config step with shell hackery.
This generic approach uses `config` CLI to tweak the .config as needed,
for example:
UBOOT_CUSTOMIZE_CONFIG := \
--enable CMD_EFIDEBUG \
--enable CMD_BOOTMENU \
--enable AUTOBOOT \
--enable AUTOBOOT_MENU_SHOW \
--disable AUTOBOOT_KEYED \
--disable AUTOBOOT_USE_MENUKEY \
--disable BOOTMENU_DISABLE_UBOOT_CONSOLE \
--set-val BOOTDELAY 2
Signed-off-by: Petr Štetiar <[email protected]>
Petr Štetiar