trusted-firmware-a.mk: pass DTC path similar to u-boot.mk

trusted-firmware-a.mk: pass DTC path similar to u-boot.mk

Instead of relying on dtc being provided by the build host use the
dtc from $(LINUX_DIR) similar to how it's done also in u-boot.mk.
For this to work kernel.mk now needs to be included before
trusted-firmware-a.mk, add this include to all affected packages.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>