Update Amlogic MMC driver:

1. Advertise the actual min / max speeds the hardware is capable of supporting given the reference clock used by the board.
2. Rather than attempting to extend the hardware's timeout register in software (the hardware doesn't have sufficient bits to directly support long timeouts), simply implement the same timeout approach

	         used in the SDXC driver.

  3) Set the timeout for a linked command (e.g. STOP TRANSMISSION) based
       on the previous multiblock read / write.

The changes have been smoke tested on both the ODROID-C1 and the VSATV102-M6
using the following cards:

• PQI 2GB microSD
• SanDisk 2GB microSD
• PQI 8GB SDHC (not a microSD so only tested on the ATV-102)
• PNY 8GB microSDHC
• SanDisk Ultra 32GB microSDHC

Submitted by: John Wehle