Add a /common dir to contain code shared by multiple BSPs in the
meta-intel repo, along with a couple recipes to live there
temporarily.

In this case, there are two BSPs that need to share the common grub2
and associated initramfs-live-install changes (sugarbay and
jasperforest).

The grub2 and associated initramfs-live-install changes will soon be
submitted to the main poky repo, but for now it makes more sense to
keep them here - they're needed for live-install of the two BSPs
mentioned, but they contain a couple hacks that need to be addressed
and are untested with anything else.

Signed-off-by: Tom Zanussi <tom.zanussi@intel.com>