reg_dumper: change and fix behavior when using dump files

reg_dumper: change and fix behavior when using dump files

Before this patch, handling dump files was wrong:
- when HAS_PCH_SPLIT was specified, intel_reg_dumper segfaulted inside
  intel_check_pch()
- the "devid" variable was used but not set
- there was no way to specify the device id of the machine used to
  generate the dump file

This patch fixes this behavior with the following changes:
- the HAS_PCH_SPLIT variable is gone
- there is now a '-d' argument that can be used to specify the device id
  used to interpret the results
- when a dump file is used but the '-d' argument is not provided, an
  Ironlake machine is assumed

Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>