u-boot: Add UBOOT_LOCALVERSION to control version string

u-boot: Add UBOOT_LOCALVERSION to control version string

* Add a variable called UBOOT_LOCALVERSION which when set will
  place a version string in the .scmversion file of the u-boot
  sources.  This string will be picked up by the u-boot Makefile
  and will be appended to the u-boot version.  This is done to
  make it easier to identify what revision of the u-boot sources
  are being run.  For example you can use a setting like the
  following to add the short commit id to the u-boot version
  string:

UBOOT_LOCALVERSION = "-g${@d.getVar('SRCPV', True).partition('+')[2][0:7]}"

(From OE-Core rev: 566298409408c6103f7a9871bb13ae5449c4fd64)

Signed-off-by: Chase Maupin <Chase.Maupin@ti.com>
Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>