coreboot arm64: Add support for arm64 into coreboot framework

Add support for enabling different coreboot stages (bootblock, romstage and
ramstage) to have arm64 architecture. Most of the files have been copied over
from arm/ or arm64-generic work.

Signed-off-by: Furquan Shaikh <furquan@google.com>
Reviewed-on: https://chromium-review.googlesource.com/197397
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Commit-Queue: Furquan Shaikh <furquan@chromium.org>
Tested-by: Furquan Shaikh <furquan@chromium.org>
(cherry picked from commit 033ba96516805502673ac7404bc97e6ce4e2a934)

This patch is essentially a squash of aarch64 changes made by
these patches:

d955885 coreboot: Rename coreboot_ram stage to ramstage
a492761 cbmem console: Locate the preram console with a symbol instead of a sect
96e7f0e aarch64: Enable early icache and migrate SCTLR from EL3
3f854dc aarch64: Pass coreboot table in jmp_to_elf_entry
ab3ecaf aarch64/foundation-armv8: Set up RAM area and enter ramstage
25fd2e9 aarch64: Remove CAR definitions from early_variables.h
65bf77d aarch64/foundation-armv8: Enable DYNAMIC_CBMEM
9484873 aarch64: Change default exception level to EL2
7a152c3 aarch64: Fix formatting of exception registers dump
6946464 aarch64: Implement basic exception handling
c732a9d aarch64/foundation-armv8: Basic bootblock implementation
3bc412c aarch64: Comment out some parts of code to allow build
ab5be71 Add initial aarch64 support

The ramstage support is the only portion that has been tested
on actual hardware. Bootblock and romstage support may require
modifications to run on hardware.

Change-Id: Icd59bec55c963a471a50e30972a8092e4c9d2fb2
Signed-off-by: Isaac Christensen <isaac.christensen@se-eng.com>
Reviewed-on: http://review.coreboot.org/6915
Tested-by: build bot (Jenkins)
Reviewed-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>
Reviewed-by: Furquan Shaikh <furquan@google.com>