ath79: move tplinkpart.c parser to patches

ath79: move tplinkpart.c parser to patches

Between 4.19 and 5.4, mtd parsers have been moved to "parsers"
subdirectory. Like for myloader.c in the previous patch,
this patch moves tplinkpart.c to the kernel patches, so the
code and the kernel includes are at the same location and
the path can be adjusted per kernel.

While at it, remove some outdated kernel version switches from
the C code.

Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>