ARM: bcm2835: remove useless variables from Makefile.boot

Neither params_phys-y nor initrd_phys-y are needed when booting with a
Device Tree. Those values are passed through the Device Tree blob. So
get rid of those variable definitions from Makefile.boot.
Signed-off-by: NThomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: NStephen Warren <swarren@wwwdotorg.org>

arch/arm/mach-bcm2835/Makefile.boot

-   zreladdr-y := 0x00008000
-params_phys-y := 0x00000100
-initrd_phys-y := 0x00800000
+zreladdr-y := 0x00008000