configs/beaglebone: update kernel/uboot, add AM335x EVM support

configs/beaglebone: update kernel/uboot, add AM335x EVM support

This patch updates the target config for the beaglebone based on the
AM335x CPU. It also supports the beagleboneblack, the TI evm and evmsk.
Device tree blobs for am335x-evm, am335x-evmsk, am335x-bone,
am335x-boneblack will be built and a sd card image is created with a
post-image script.  The kernel and driver versions match the
ti-processor-sdk 02.00.00.00.  Patches allow the use of old AM335x evm
revisions (1 bit sd card) and JTAG debugging.

Kernel JTAG patch: By default the kernel will disable the JTAG clock,
access via the JTAG port will not work after the kernel booted. The
AM335x-evm has a JTAG header fitted, this patch keeps the JTAG clock
alive.

Signed-off-by: Lothar Felten <lothar.felten@gmail.com>
[Thomas: remove 1-bit MMC patch, it's causing a significant performance
regression for users of BeagleBone, which are 99.99% of the users of
this defconfig.]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>