build: sort bootloader image sources

To avoid duplicate symbol errors when compiling bootloader images which
pull in the same source file multiple times, sort source files before
generating bootloader image build rules in order to remove duplicates.

Change-Id: I03a60d9f752f8fe85f17ec14e265fd4a6223de32
Signed-off-by: Chris Kay <chris.kay@arm.com>
1 file changed