kconfig: Add support for 'as-option'

Currently kconfig does not have a feature that allows to detect if the
used assembler supports a specific compilation option.

Introduce 'as-option' to serve this purpose in the context of Kconfig:

        config X
                def_bool $(as-option,...)

Signed-off-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Acked-by: Masahiro Yamada <masahiroy@kernel.org>
Cc: linux-kbuild@vger.kernel.org
Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>