Build system: Trigger dependency checking only for build targets
Build system: Trigger dependency checking only for build targets

The Makefile used to specify a blacklist of rules for which
dependency checking must not be triggered.  This list included
cleaning rules only, whereas all other non-build targets (e.g.
help, checkpatch, etc.) should also be included.

This approach seems a bit fragile because it is easy to forget
some non-building rules in the blacklist, as the experience
showed us.  It is more robust to specify a whitelist of rules
for which dependency checking is required.

Fixes ARM-software/tf-issues#112

Change-Id: I030c405abb35972a726a5200396430316d18f963

lsigithub/arm-trusted-firmware_public,idl3r/arm-trusted-firmware,idl3r/arm-trusted-firmware,sandrine-bailleux-arm/arm-trusted-firmware,yatharth-arm/arm-trusted-firmware,sbranden/arm-trusted-firmware,hzhuang1/arm-trusted-firmware,yatharth-arm/arm-trusted-firmware,jforissier/arm-trusted-firmware,vchong/arm-trusted-firmware,athoelke/arm-trusted-firmware,sandrine-bailleux-arm/arm-trusted-firmware,achingupta/arm-trusted-firmware,davwan01/arm-trusted-firmware,jcastillo-arm/arm-trusted-firmware,robixnai/arm-trusted-firmware,athoelke/arm-trusted-firmware,sandrine-bailleux/arm-trusted-firmware,sandrine-bailleux/arm-trusted-firmware,jforissier/arm-trusted-firmware,lsigithub/arm-trusted-firmware_public,mtk09422/arm-trusted-firmware,mtk09422/arm-trusted-firmware,davwan01/arm-trusted-firmware,vikramkanigiri/arm-trusted-firmware,vchong/arm-trusted-firmware,ljerry/arm-trusted-firmware,Leo-Yan/arm-trusted-firmware,achingupta/arm-trusted-firmware,Leo-Yan/arm-trusted-firmware,robixnai/arm-trusted-firmware,vikramkanigiri/arm-trusted-firmware,96boards/arm-trusted-firmware,hzhuang1/arm-trusted-firmware,96boards/arm-trusted-firmware,jcastillo-arm/arm-trusted-firmware,sbranden/arm-trusted-firmware,longsleep/arm-trusted-firmware-pine64,ljerry/arm-trusted-firmware,longsleep/arm-trusted-firmware-pine64