intel_pmc_ipc: Fix GCR register base address and length

GCR register (pmc_cfg register) is at offset 0x1008, and
remapping of 0x4 bytes is enough.

Signed-off-by: Francois-Nicolas Muller <francois-nicolas.muller@intel.com>
Signed-off-by: Qipeng Zha <qipeng.zha@intel.com>
Acked-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Darren Hart <dvhart@linux.intel.com>