Bug Fix: Fix checkpatch rule in Makefile
Bug Fix: Fix checkpatch rule in Makefile

The shell command used to list all files but the libc's ones
introduced in commit 95d5353c33 was incorrect. It was listing
subdirectories without referencing their parent directories.
This patch fixes it.

Also, the command used to invoke the checkpatch.pl script is now
printed when V=1.

Change-Id: Ie2f1e74f60d77e38c25e717cffa44ca03baec7b2
davwan01/arm-trusted-firmware,lsigithub/arm-trusted-firmware_public,idl3r/arm-trusted-firmware,achingupta/arm-trusted-firmware,sbranden/arm-trusted-firmware,athoelke/arm-trusted-firmware,jcastillo-arm/arm-trusted-firmware,achingupta/arm-trusted-firmware,sbranden/arm-trusted-firmware,sandrine-bailleux-arm/arm-trusted-firmware,davwan01/arm-trusted-firmware,lsigithub/arm-trusted-firmware_public,mtk09422/arm-trusted-firmware,sandrine-bailleux-arm/arm-trusted-firmware,sandrine-bailleux/arm-trusted-firmware,sandrine-bailleux/arm-trusted-firmware,athoelke/arm-trusted-firmware,idl3r/arm-trusted-firmware,robixnai/arm-trusted-firmware,mtk09422/arm-trusted-firmware,robixnai/arm-trusted-firmware,jcastillo-arm/arm-trusted-firmware