BeagleBoard: make Beagle use GPTIMER12 for system ticks

BeagleBoard: make Beagle use GPTIMER12 for system ticks

There is suspicion that the 32kHz input clock to the OMAP may be noisy
on BeagleBoards.  On OMAP2/3 GPTIMER1, this can cause the timer
counter register to warp to unknown values or miss interrupt
conditions.  So, use GPTIMER12 instead, which apparently has its own
secure 32kHz oscillator and will hopefully not be prone to the
suspected sys_32k glitches.

This is only a workaround.  If sys_32k is noisy, other system peripherals
may be affected.

This workaround is a collective product of several people, most notably
Philip Balister <philip@balister.org>, Dirk Behme <dirk.behme@googlemail.com>,
Koen Kooi <k.kooi@student.utwente.nl>, Tony Lindgren <tony@atomide.com>,
Steve Sakoman <sakoman@gmail.com>, Khasim Syed Mohammed <khasim@ti.com>
Richard Woodruff <r-woodruff2@ti.com>, Kevin Hilman <khilman@deeprootsystems.com>.
I apologize if there is anyone whom I've missed.

Signed-off-by: Paul Walmsley <paul@pwsan.com>
Cc: Khasim Syed Mohammed <khasim@ti.com>
Cc: Koen Kooi <k.kooi@student.utwente.nl>
Cc: Steve Sakoman <sakoman@gmail.com>
Cc: Richard Woodruff <r-woodruff2@ti.com>
Cc: Tony Lindgren <tony@atomide.com>
Cc: Philip Balister <philip@balister.org>
Cc: Dirk Behme <dirk.behme@googlemail.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>