Correct ARM Versatile Timer Initialization

 - According to ARM Dual-Timer Module (SP804) TRM (ARM DDI0271),
   -- Timer Value Register @ TIMER Base + 4 is Read-only.
   -- Prescale Value (Bits 3-2 of TIMER Control register)
	can only be one of 00,01,10. 11 is undefined.
   -- CFG_HZ for Versatile board is set to
	#define CFG_HZ		(1000000 / 256)
	So Prescale bits is set to indicate
	- 8 Stages of Prescale, Clock divided by 256
 - The Timer Control Register has one Undefined/Shouldn't Use Bit
   So we should do read/modify/write Operation

Signed-off-by: Gururaja Hebbar <gururajakr@sanyo.co.in>