Various fixes to the ti_sdhci driver, mostly to make it work on Pandaboard.

 - Don't allow high-speed mode on OMAP4 due to hardware erratum.
 - Check the proper bit in the status register when waiting for the
   controller to come out of reset.
 - Add handling for the "non-removable" fdt property by always returning
   "card is present" status.
 - Add the non-removable property for the MMC card on a Beaglebone Black.
 - Add the non-removable property for Pandaboard as a workaround.

For Pandaboard the card detect pin is handled by the twl6030 fpga device
which gets an interrupt on pin change and then has to query the fpga
for the actual status.  We don't have code to do that yet.

Submitted by:	Svatopluk Kraus <onwahe@gmail.com>
When changing the sd bus clock divisor, clear just the bus clock enable bit
before changing the divisor bits in the register.  We were writing a zero
to the register, which clears the enable, but also cleared the divisor bits
at the same time.  That's a violation of the sdhci spec, which says the
divisor can only be changed when the clock is disabled.  This has worked
okay on most hardware for years, but the TI OMAP controller would misbehave
after changing the divisor improperly.

Submitted by:	Svatopluk Kraus <onwahe@gmail.com>