SPI: Merge improved clock management from N800 tree into OMAP2 McSPI

Patch makes the OMAP2 McSPI module to use interface and functional clocks
only when needed and inserts timeout handling in function
omap2_mcspi_txrx_pio.

These are originally developed by Samuel Ortiz <samuel.ortiz@solidboot.com>
and Juha Yrjola <juha.yrjola@solidboot.com>.

Signed-off-by: Jarkko Nikula <jarkko.nikula@nokia.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>