ACPI: Avoid array address overflow when _CST MWAIT hint bits are set

The Cx Register address obtained from the _CST object is used as the MWAIT
hints if the register type is FFixedHW. And it is used to check whether
the Cx type is supported or not.

On some boxes the following Cx state package is obtained from _CST object:
    >{
                ResourceTemplate ()
                {
                    Register (FFixedHW,
                        0x01,               // Bit Width
                        0x02,               // Bit Offset
                        0x0000000000889759, // Address
                        0x03,               // Access Size
                        )
                },

                0x03,
                0xF5,
                0x015E }

   In such case we should use the bit[7:4] of Cx address to check whether
the Cx type is supported or not.

mask the MWAIT hint to avoid array address overflow

Signed-off-by: Zhao Yakui <yakui.zhao@intel.com>
Acked-by: Venki Pallipadi <venkatesh.pallipadi@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>