arm:mmc driver refactor.

Generalize the usage of mmc_send_cmd function to allow
it to transfer data and remove direct invocations to
mmchs_send_cmd.

Change-Id: Iabb9a7d3f4ec57536407b369531ded2b8b649cce
arm timer fix

	. set 'done' once initialized so 32-bit read frc works,
	  thanks to keesj
	. make sure the software-implemented upper 32 bit of the 64-bit
	  "tsc" value works OK by adding an assert in one of its calls

Change-Id: I5ce24fea919f4610c6a86ac7ec9f04b1815620c2
padconf: remove duplicate code.

The same code block was repeated twice (copy & paste error).

Change-Id: I2035c9fff46b3f0a52084c2d6c871bbda6f8f07f
arm:mmc driver refactor and timeout fix for BeagleBoneBlack.

When we send MMC commads that contain data the controller provides no
description of the order of events and we need to be able to send data
from and to the controller "when needed". Changed the code to react
on buffer read and buffer write ready based on interrupts.

Change-Id: I60c9140bf0e45b74be6475054564d4e1bd89f21e
arm:increase the mmc driver process priority.

Increase driver process priority to prevent starvation. Without
special attribute drivers will have the same priority as other
userland processes this. Posix test 1 was taking so much resources
that it triggered alarms in the MMC driver.

Change-Id: Icd3295d8f2a4a284418327a3715641fe9a3b3043
build:arm remove "start usb" from u-boot command line.

Removed "start usb" from u-boot command line as it is not needed and
speeds up tftp booting.

Change-Id: I416f7eb0467888d1b69ef3dad09df0639fb63f10
arm:use the 4 bit mmc data bus if supported by the card.

Change-Id: I55de05db23ad1766e5faec93252e8410cbf59001