arch/riscv: Update encoding.h and dependent files

I copied it from commit e10d2def7d of spike and made sure the copyright
header is still there.

Change-Id: Ie8b56cd2f4855b97d36a112a195866f4ff0feec5
Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Reviewed-on: https://review.coreboot.org/15832
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
3 files changed