mips: vdso: Use generic VDSO clock mode storage

Switch to the generic VDSO clock mode storage.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Link: https://lkml.kernel.org/r/20200207124403.244684017@linutronix.de