Build: add -MP option to add dummy rules to *.d files
Build: add -MP option to add dummy rules to *.d files

This adds a phony target for each dependency other than the main
file, causing each to depend on nothing.

Without this, the incremental build will fail when a header file
is removed.

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

achingupta/arm-trusted-firmware,lsigithub/arm-trusted-firmware_public,sbranden/arm-trusted-firmware,achingupta/arm-trusted-firmware,lsigithub/arm-trusted-firmware_public,sbranden/arm-trusted-firmware