PXA27x support

[David Vrabel]

The attached patch adds (some) support for PXA27x processors to the
pxa2x0 HAL.  Limited to some extra register #defines and support for the
extra interrupts on the PXA27x.

A new CDL option (CYGOPT_HAL_ARM_XSCALE_PXA2X0_VARIANT) to the pxa2x0
HAL to select which variant of the pxa2xx family to support, either
PXA25x (the default) or PXA27x.

Additionally, hal_delay_us() will busy-wait for the correct period of
time if it takes longer than 1 timer tick per loop to read the counter
register.

David Vrabel
-- 
David Vrabel, Design Engineer

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