x86/resctrl: Rename and change the units of resctrl_cqm_threshold

resctrl_cqm_threshold is stored in a hardware specific chunk size,
and exposed to user-space.

This means the filesystem parts of resctrl need to know how the hardware
counts, to convert the user provided byte value to chunks. The interface
between the architecture's resctrl code and the filesystem ought to
treat everything as bytes.

Change the unit of resctrl_cqm_threshold to bytes. resctrl_arch_rmid_read()
still returns its value in chunks, so this needs converting to bytes.
As all the callers have been touched, rename the variable to
resctrl_rmid_realloc_threshold, which describes what the value is for.

Signed-off-by: James Morse <james.morse@arm.com>