OMAP2/3 GPTIMER: skip unnecessary TLDR write during non-autoreload

OMAP2/3 GPTIMER: skip unnecessary TLDR write during non-autoreload

The GPTIMER TLDR register does not need to be written if the GPTIMER
is not in autoreload mode.  This is the usual case for dynamic tick-enabled
kernels.

Simulation data indicate that skipping the read that occurs as part of
the write should save at least 300-320 ns for each GPTIMER1 timer
reprogram.  (This assumes L4-Wakeup is at 19MHz and GPTIMER write
posting is enabled.)  Skipping the write itself probably won't have
much impact since it should be posted on the OCP interconnect.

Tested on 2430SDP and 3430SDP.

Signed-off-by: Paul Walmsley <paul@pwsan.com>
Cc: Richard Woodruff <r-woodruff2@ti.com>
Acked-by: Kevin Hilman <khilman@deeprootsystems.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>