i2c: pxa: Add support for pxa910/988 & new configuration features

TWSI_ILCR & TWSI_IWCR registers are used to adjust clock rate
of standard & fast mode in pxa910/988; so this patch adds these two new
entries to "struct pxa_reg_layout" and "struct pxa_i2c".

Signed-off-by: Jett.Zhou <jtzhou@marvell.com>
Signed-off-by: Yi Zhang <yizhang@marvell.com>
Signed-off-by: Vaibhav Hiremath <vaibhav.hiremath@linaro.org>
Tested-by: Robert Jarzmik <robert.jarzmik@free.fr>
[wsa: white space fixes]
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>