…specific gap fill

Deprecate BUILD_NO_GAP_FILL as it gives a false impression that gap
filling can be disabled in binary files.
Binary files are always gap filled due to the fact they contain no
address information. Only option for binary files is to control the gap
fill pattern. When no gap fill is enabled in binary files, then a
default pattern is used by the tool, which usually is 0x00.

Generally the pattern 0x00 leads to unnecessary flash writes, as a
flash generally contains 0xFF after an erase.
Therefore provide a gap fill pattern Kconfig setting instead, with
default value of 0xFF.

For hex-files, intel hex and s19, then gap filling is generally not
needed but in order to still support cases where gap filling is required
then this commit introduces BUILD_OUTPUT_HEX_GAP_FILL and
BUILD_OUTPUT_S19_GAP_FILL. Both settings are disabled per default.

Signed-off-by: Torsten Rasmussen <[email protected]>
(cherry picked from commit 2e8868c)