riscv: bring in the configstring parsing functions from UCB

I've tested this with commits to come later.

This is from the lowrisc bbl distribution, 87588c4,
with fixes so it builds.

Change-Id: I87893638872259c94d6972e1971578b633155e7e
Signed-off-by: Ronald G. Minnich <rminnich@gmail.com>
Reviewed-on: https://review.coreboot.org/17255
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
2 files changed