Minor tweak to the new DaVinci clock code:  look at the PSC module
to make sure the clock is enabled before reporting that it needs
disabling.  This improves the value of those diagnostics.

Docs report a variety of power-up states for peripherals.  DM355
seems to leave most things clocked (but in reset); else, most
clocks will still be off unless the bootloader enabled them.

Also includes a minor fix to the MDCTL write:  DM355 defines
that field as five bits; other cores define the extra bits as
must-be-zero.
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>