MFD,mmc: tmio_mmc: make HCLK configurable

The Toshiba parts all have a 24 MHz HCLK, but HTC ASIC3 has a 24.576 MHz HCLK
and AMD Imageon w228x's HCLK is 80 MHz. With this patch, the MFD driver
provides the HCLK frequency to tmio_mmc via mfd_cell->driver_data.

Signed-off-by: Philipp Zabel <philipp.zabel@gmail.com>
Acked-by: Ian Molton <ian@mnementh.co.uk>
Acked-by: Samuel Ortiz <sameo@openedhand.com>
Signed-off-by: Pierre Ossman <pierre@ossman.eu>