Patch from Liam Girdwood

This patch updates the pxa2xx channel map registers definitions in
pxa-regs.h

Changes:-
  o Added description for SSP2 registers
  o Added definitions for SSP3 registers
Signed-off-by: NLiam Girdwood <liam.girdwood@wolfsonmicro.com>
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>