cxl/hdm: Skip emulation when driver manages mem_enable

cxl/hdm: Skip emulation when driver manages mem_enable

If the driver is allowed to enable memory operation itself then it can
also turn on HDM decoder support at will.

With this the second call to cxl_setup_hdm_decoder_from_dvsec(), when
an HDM decoder is not committed, is not needed.

Fixes: b777e9bec960 ("cxl/hdm: Emulate HDM decoder from DVSEC range registers")
Link: http://lore.kernel.org/r/20230220113657.000042e1@huawei.com
Reported-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Tested-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Fan Ni <fan.ni@samsung.com>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Link: https://lore.kernel.org/r/167703068474.185722.664126485486344246.stgit@dwillia2-xfh.jf.intel.com
Signed-off-by: Dan Williams <dan.j.williams@intel.com>