[MIPS] Create consistency in "system type" selection.

The "system type" Kconfig options on MIPS are not consistent.  For
some platforms, only the name is listed while other entries are
prepended with "Support for".  Remove this as it doesn't make sense
when describing the "system type".

Signed-off-by: Martin Michlmayr <tbm@cyrius.com>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>