Make:Add realclean to .PHONY list
Make:Add realclean to .PHONY list

Update the cert_create Makefile to list realclean as .PHONY
(like clean)

Change-Id: I9dc8a61a11574a044372e0952b5b12b74e133747

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