msm: perf: Refine disable/enable in tracecounters

Tracecounter code was not disabling counters as early as possible
and enabling them as late as possible. Refine the logic so cycles
spent inside the handler are as lower. This results in more accurate
per-process counter values.

Change-Id: Ib8bb17b1212ddf9e3d1c33a00ae486d885a36e45
Signed-off-by: Sheetal Sahasrabudhe <sheetals@codeaurora.org>

Conflicts:
	arch/arm/mach-msm/perf_debug.c