ACPI: Fix ioremap size for MMIO reads and writes

The size used for I/O remapping MMIO read and write accesses has not
accounted for the basis of ACPI's Generic Address Structure (GAS)
'Register Bit Width' field which is bits, not bytes.  This patch
adjusts the ioremap() 'size' argument accordingly.

ACPI "Generic Register" reference:
  ACPI Specification, Revision 4.0, Section 5.2.3.1, "Generic Address
  Structure".

Signed-off-by: Myron Stowe <myron.stowe@hp.com>
Signed-off-by: Len Brown <len.brown@intel.com>