Add lost Kconfig symbol.  This should have been part of 40e084a5
('MIPS: Add uprobes support.').

Fixes: 40e084a5 ('MIPS: Add uprobes support.')
Signed-off-by: Marcin Nowakowski <marcin.nowakowski@imgtec.com>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>