Makefile: repair CONFIG_CC_OPTIMIZE_FOR_DEBUG support

Makefile: repair CONFIG_CC_OPTIMIZE_FOR_DEBUG support

Since commit 5f520875bdf0 ("kbuild: Bump the build system to 5.1")
CONFIG_CC_OPTIMIZE_FOR_DEBUG has no effect on the non-host code.

This patch reestablishes the prior logic to add

    -Og -Wno-maybe-uninitialized

to KBUILD_CFLAGS.

Fixes: 5f520875bdf0 ("kbuild: Bump the build system to 5.1")
Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>