platform: generic-arm64: Add dtb boot support

Add support for boot protocol with dtb in x0 instead of ram size. Find
gic (v3) registers in device tree instead of making an smc call.

TODO: Add gicv2 support

Bug: 297275002
Change-Id: Ie30b71cb6b7897438bf953b04ad1f41583ce6d97
2 files changed