MIPS: Kconfig: Fix the arch-specific header path

The header path in the help text for the RUNTIME_DEBUG config option is
obsolete and needs to be updated to match the new location of
architecture-specific header files. While at it, fix the spelling mistake.

Signed-off-by: Dmitri Vorobiev <dmitri.vorobiev@movial.fi>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>