Port yaboot logic for various powerpc machine types

Port yaboot logic for various powerpc machine types

Some powerpc machines require not updating the NVRAM.  This can be handled
by existing grub-install command-line options, but it's friendlier to detect
this automatically.

On chrp_ibm machines, use the nvram utility rather than nvsetenv.  (This
is possibly suitable for other machines too, but that needs to be
verified.)

Forwarded: no
Last-Update: 2014-10-15

Patch-Name: install-powerpc-machtypes.patch