kernel: drop Fon(Foxconn) parser matching for the "firmware" partition

kernel: drop Fon(Foxconn) parser matching for the "firmware" partition

This parser's matching function appears to be too generic as it matches
e.g. Buffalo WZR-HP-G300NH. That results in incorrect parts parsing.

Luckily this parser is needed by Fon FON2601 only which uses DT-based
ramips target. It means we can depend on mtd subsystem matching of
"fonfxc,uimage" string.

That said triggering this parser based on the "firmware" (or whatever
MTD_SPLIT_FIRMWARE_NAME is) partiiton name is not needed. It can be
dropped which will automatically fix the Buffalo WZR-HP-G300NH case.

Fixes: a1c6a316d299 ("ramips: add support for Fon FON2601")
Signed-off-by: Rafał Miłecki <rafal@milecki.pl>