[ARM] pxa: make pxa2xx_spi driver use ssp_request()/ssp_free()

1. make pxa2xx_spi.c use ssp_request() and ssp_free() to get the common
   information of the designated SSP port.

2. remove those IRQ/memory request code, ssp_request() has done that for
   the driver

3. the SPI platform device is thus made psuedo, no resource (memory/IRQ)
   has to be defined, all will be retreived by ssp_request()

4. introduce ssp_get_clk_div() to handle controller difference in clock
   divisor setting

5. use clk_xxx() API for clock enable/disable, and clk_get_rate() to
   handle the different SSP clock frequency between different processors

Signed-off-by: eric miao <eric.miao@marvell.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>