Add script to build powernv/pseries/mtd_block/powernv_flash vmlinux
Add script to build powernv/pseries/mtd_block/powernv_flash vmlinux

This script is heavily based off the preexisting kernel-build.sh script

Change-Id: If6f1a86d8d3195ede1da32cc01ddcfb6233714c5
Signed-off-by: Cyril Bur <6ce38dade8c4b52fd55c193fae70fd1d1275c3c3@au1.ibm.com>

openbmc/openbmc-build-scripts,openbmc/openbmc-build-scripts