[DRA7][STATCOLL] Add DRA7 specific statistics collector library

The statistics collectors (statcoll) on the L3 NoC allow for hardware monitoring
of traffic statistics on the EMIF bus. This patch adds support for
accessing the DRA7xx statistics collectors using the trace bw feature.

Example:
$./omapconf trace bw -m dss
Monitors read and write traffic to DSS.

$./omapconf trace bw -h
Displays help text.

Signed-off-by: Edward Shin <e-shin@ti.com>
Signed-off-by: Nishanth Menon <nm@ti.com>