BeagleBone Black support

[gsmcmullin]

The BeagleBone black is a low cost board based on the TI AM335x Cortex-A8.
The existing support for Cortex-A in BMP should work with this core, except that the ADIv5 JTAG-DP is not directly exposed, it's hidden behind the 'ICEPICK Module'.

To expose the JTAG-DP on the scan chain:

• the JTAG chain must be scanned to detect the ICEPICK
• the ICEPICK must be configured to connect the JTAG-DP in the scan chain
• the chain must be rescanned to detect the JTAG-DP

The fact that the topology of the scan chain changes dynamically is problematic. The current scan code in BMP resets the JTAG logic, which will disconnect the JTAG-DP. Some refactoring around JTAG scanning and reset abstraction will be needed before this support can be added.

[gsmcmullin]

AM335x TRM: http://www.ti.com/lit/pdf/spruh73
ICEPICK_D config info: http://processors.wiki.ti.com/images/f/f6/Router_Scan_Sequence-ICEpick-D.pdf
TI Wiki page: http://processors.wiki.ti.com/index.php/ICEPICK