ACPI: MRRM: Fix default max memory region

Per the spec, the default max memory region must be 1 covering
all system memory.

When platform does not provide ACPI MRRM table or
when CONFIG_ACPI is opted out, the acpi_mrrm_max_mem_region() function
defaults to  returning 1 region complying to RDT spec.

Signed-off-by: Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Link: https://patch.msgid.link/20250523172001.1761634-1-anil.s.keshavamurthy@intel.com


Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>