time: x86: Replace LATCH with PIT_LATCH in i8253 clocksource driver

time: x86: Replace LATCH with PIT_LATCH in i8253 clocksource driver

The i8253 clockevent & clocksource driver uses PIT_LATCH
except for two cases where it uses LATCH:

1)
	/* VIA686a test code... reset the latch if count > max + 1 */
	if (count > LATCH) {

LATCH is based on CLOCK_TICK_RATE which is defined as
PIT_TICK_RATE on x86 so this should just be the later.

2)
	...
	switch (mode) {
	case CLOCK_EVT_MODE_PERIODIC:
		/* binary, mode 2, LSB/MSB, ch 0 */
		outb_p(0x34, PIT_MODE);
		outb_p(LATCH & 0xff , PIT_CH0);	/* LSB */
		outb_p(LATCH >> 8 , PIT_CH0);		/* MSB */
	...

MIPS and ARM are the only other arches that use this driver. In
the MIPS case CLOCK_TICK_RATE is defined as the same value as
PIT_TICK_RATE. For ARM, the only machine that uses it is
Footbridge which has a totally bogus CLOCK_TICK_RATE according
to the comments. Furthermore, the clockevent_i8253_init()
initializes the clockevent with PIT_TIC_RATE, so there's
no reason to use the generic LATCH.

This is part of work to remove and depecrate the global
CLOCK_TICK_RATE symbol.

Signed-off-by: Deepak Saxena <dsaxena@linaro.org>
Signed-off-by: John Stultz <john.stultz@linaro.org>