armsr: armv8: enable Broadcom arch'es

armsr: armv8: enable Broadcom arch'es

This is part of an effort to reduce differences between
the OpenWrt armsr/armv8 config and Linux arm64 defconfig.

This enables CONFIG_ARCH_BCM and downstream
CONFIG_ARCH_BCM2835 (= BCM2711 like Raspberry Pi 4)
and CONFIG_ARCH_BCM_IPROC (Broadcom iProc packet processors).

The broadband specific SoC's (ARCH_BCMBCA) are left out
as it is assumed these will not be doing EFI boot.

Signed-off-by: Mathew McBride <matt@traverse.com.au>
(23.5/5.15 version of commit df23eed17925b8cadccec53a784a12468a8a2e85)