L24.6-p3 tag

Adding the following changes since L24.6-p2:

commit e95f3d8ed80731ce4d6fcaeedc9c5e8c85d3ea6b
Author: Vikram Pandita <vikram.pandita@ti.com>

    omap-serial: driver: fix EFR read

commit c46832289acb80870c790ff03788aa352a1b0987
Author: Kishore Kadiyala <kishore.kadiyala@ti.com>

    Adding dummy power & Sleep functions for MMC5

Also modifications to Release_Notes, adding as a prerequisite
to add the 'mkimage' path to PATH variable before to try to
compile the Kernel uImage.