mmc: add Toshiba PCI SD controller driver

This patch resurrects an old never-finished driver for Toshiba PCI SD
controllers found in some older Toshiba laptops (such as Portege R100):

02:0d.0 System peripheral [0880]: Toshiba America Info Systems SD TypA Controller [1179:0805] (rev 05)

The code is fixed, cleaned up and successfully tested with SD, SDHC, SDXC and
MMC cards on Portege R100. (MMC cards don't even work in Windows!)
SDIO probably does not work (don't have any SDIO card).

The hardware is slow (around 2 MB/s - same in Windows) because it does not
support bus mastering (busmaster enable bit cannot be set in PCI control reg).
Also the card clock is limited to 16MHz (33MHz PCI clock divided by 2).

Signed-off-by: Ondrej Zary <linux@rainbow-software.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>