u-boot inc: update inc file for newer u-boot versions

u-boot inc: update inc file for newer u-boot versions

* Add support for different suffixes found with later u-boot
  versions which have switched from .bin to .img
* Allow recipes that include u-boot.inc to also package an
  SPL if they build one.
    * Minimum requirement is to set the SPL_BINARY value to add
      the SPL to the u-boot package as well as into the deploy
      directory.

(From OE-Core rev: 2965aa2faaccce43f6c3e451c0a2ded3734766e4)

Signed-off-by: Chase Maupin <Chase.Maupin@ti.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>