intel_reg_dumper: enable the power well

intel_reg_dumper: enable the power well

The intel_reg_dumper tool reads a lot of display registers. If we
don't turn on the power well, dmesg will get flooded with tons of
messages about unclaimed registers. So here we enable the "Debug"
power well register and then restore its state later. It's impossible
to guarantee that other things won't mess with the debug register
between our put and get calls, but at least we're trying our best to
keep things working fine, and it's the debug register anyway.

As far as I know, nothing else uses the Debug register for anything,
so we should be safe for now.

Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>