The Entire Flash (EF) image for revo has a gap between
the end of the BL bank and the start of the FW bank.
This fills the gap with 0xFF and properly aligns the
FW image in flash.
A separate makefile for EF (Entire Flash) targets allows
the removal of board-specific hard-coded addresses. These
values can now be included from the board-info.mk files
for each board.