RISCV: get RISCV to build again

This makes lzmadecode 64-bit clean (I hope).
It also cleans up a few other nits.

Change-Id: I24492e9f357e8d3a6de6abc351267f900eb4a19a
Signed-off-by: Ronald G. Minnich <rminnich@gmail.com>
Reviewed-on: http://review.coreboot.org/7623
Reviewed-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
Tested-by: build bot (Jenkins)