refactor(fiptool): move plat_fiptool.mk to tools

refactor(fiptool): move plat_fiptool.mk to tools

Move all plat_fiptool.mks into tools, change the logic to recursively
check for tools/fiptool/plat_fiptool/<plat_path>/plat_fiptool.mk

I.e. for a platform that has the path "plat/arm/board/tc/platform.mk",
the makefile will now load the first existing file from:
 - tools/fiptool/plat_fiptool/arm/board/tc/plat_fiptool.mk
 - tools/fiptool/plat_fiptool/arm/board/plat_fiptool.mk
 - tools/fiptool/plat_fiptool/arm/plat_fiptool.mk

This enables fiptool to support multiple platforms, or a specific one.

Remove file-copying previously being used to handle old default path.
Remove custom file cleaning in plat_fiptool.mk.

Change-Id: I95245bcf7143b329481d4394ab64f29bfe9de5ab
Signed-off-by: Raef Coles <raef.coles@arm.com>