MIPS: vdso: Compile high resolution parts conditionally

If neither the R4K nor the GIC timer is enabled in the kernel configuration
then let the core VDSO code drop the high resolution parts at compile time.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Link: https://lkml.kernel.org/r/20200207124402.714585315@linutronix.de