Build: specify check_* targets as .PHONY
Build: specify check_* targets as .PHONY

check_* targets just check necessary command line argument, not
build any images.  They should be specified as .PHONY.

Signed-off-by: Masahiro Yamada <378b411a8a63ecc7605ec4272234862d7781c6ae@socionext.com>

achingupta/arm-trusted-firmware,achingupta/arm-trusted-firmware