cxl/region: Test CXL_DECODER_F_NORMALIZED_ADDRESSING as a bitmask

The CXL decoder flags are defined as bitmasks, not bit indices.
Using test_bit() to check them interprets the mask value as a bit
index, which is the wrong test.

For CXL_DECODER_F_NORMALIZED_ADDRESSING the test reads beyond the
flags word, making the flag sometimes appear set and blocking creation
of CXL region debugfs attributes that support poison operations.

Replace test_bit() with a bitmask check.

Found with cxl-test.

Fixes: 208f432406b7 ("cxl: Disable HPA/SPA translation handlers for Normalized Addressing")
Signed-off-by: Alison Schofield <alison.schofield@intel.com>
Reviewed-by: Gregory Price <gourry@gourry.net>
Tested-by: Gregory Price <gourry@gourry.net>
Link: https://patch.msgid.link/63fe4a6203e40e404347f1cdc7a1c55cb4959b86.1771873256.git.alison.schofield@intel.com
Signed-off-by: Dave Jiang <dave.jiang@intel.com>