meta-openpower: host-fw: New recipe to include the host firmware

This recipe will be used to bundle the bmc and host firmware into a
single image file.

The location of the host firmware image can be specified via variables.
If no host firmware image is specified, still create the default
destination directory, to mimic a blank PNOR device.

(From meta-openpower rev: d552bf6e0cf9cc1c9d4bfd650cf2765277cda980)

Change-Id: I4719cce17ae947610691a38cb0dc48ce7011db14
Signed-off-by: Adriana Kobylak <anoo@us.ibm.com>
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>