boot: Introduce BOOTSTD_MENU to control bootflow menu build

boot: Introduce BOOTSTD_MENU to control bootflow menu build

The bootflow_menu.c code depends on e.g. scene_txt_set_font(),
which is only built when CONFIG_EXPO is enabled. Introduce new
Kconfig symbol BOOTSTD_MENU which depends on EXPO to prevent
triggering errors like these in case e.g. CONFIG_VIDEO=n :

"
boot/bootflow_menu.c:158:(.text+0x8851): undefined reference to `scene_txt_set_font'
"

Make the symbol depend on BOOTSTD_FULL as well to get rid of
the Makefile dependency workaround. Since BOOTSTD_FULL is not
available in SPL, do not define SPL variant of BOOTSTD_MENU.

Fix up bootflow test accordingly.

Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
Reviewed-by: Simon Glass <sjg@chromium.org>