ARM: pxa: Remove unused clock_enable field from struct pxa2xx_spi_master

Use for struct pxa2xx_spi_master clock_enable field was removed years ago
from the pxa2xx-spi driver by the commit 2f1a74e5a2 ("[ARM] pxa: make
pxa2xx_spi driver use ssp_request()/ssp_free()").

Therefore remove it from structure definition, documentation and from
couple affected board files.

Signed-off-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Acked-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>

arch/arm/mach-pxa/z2.c

@@ -595,13 +595,11 @@ static struct spi_board_info spi_board_info[] __initdata = {
 };
 
 static struct pxa2xx_spi_master pxa_ssp1_master_info = {
-	.clock_enable	= CKEN_SSP,
 	.num_chipselect	= 1,
 	.enable_dma	= 1,
 };
 
 static struct pxa2xx_spi_master pxa_ssp2_master_info = {
-	.clock_enable	= CKEN_SSP2,
 	.num_chipselect	= 1,
 };