riscv-trap-handling: Add preliminary trap handling for riscv

RISCV requires a trap handler at the machine stage to deal with
misaligned loads/stores, as well as to deal with calls that a linux
payload will make in its setup. Put required assembly for jumping
into and out of a trap here to be set up by the bootblock in a later

Change-Id: Ibf6b18e477aaa1c415a31dbeffa50a2470a7ab2e
Signed-off-by: Thaminda Edirisooriya <thaminda@google.com>
Reviewed-on: http://review.coreboot.org/11367
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>
Tested-by: build bot (Jenkins)
2 files changed