SPARC: Emulation of GRLIB GPTimer

This device exposes three parameters:
 - frequency (uint32) : The system frequency
 - irq-line  (uint32) : IRQ line number for the first timer
                        (others use irq-line + 1, irq-line + 2...)
 - nr-timers (uint32) : Number of timers

Emulation of GrLib devices is base on the GRLIB IP Core User's Manual:
http://www.gaisler.com/products/grlib/grip.pdf

Signed-off-by: Fabien Chouteau <chouteau@adacore.com>
Signed-off-by: Blue Swirl <blauwirbel@gmail.com>
