arm: RTIC kernel integration to generate MP DTS

With new Boot Image header v2 the boot image header generation
decoupled from the kernel. RTIC DTS requires kernel build
environment (because of OBJDUMP, OBJCPY, and other dependencies).
The RTIC DTS will be compiled to DTB later either by
arch/arm64/boot/Makefile (for Boot Image Header v1) or by
kernel_definitions.mk (for Boot Image Header v2).

Change-Id: I3bf083d909b4e64d0f3dbea97c8c0ad8ee474798
Signed-off-by: James Shao <jameshao@codeaurora.org>