x86/resctrl: Merge AMD/Intel parse_bw() calls

Now after arch_needs_linear has been added, the parse_bw() calls are
almost the same between AMD and Intel.

The difference is '!is_mba_sc()', which is not checked on AMD. This
will always be true on AMD CPUs as mba_sc cannot be enabled as
is_mba_linear() is false.

Removing this duplication means user-space visible behaviour and
error messages are not validated or generated in different places.

Reviewed-by : Babu Moger <babu.moger@amd.com>
Signed-off-by: James Morse <james.morse@arm.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
Link: https://lkml.kernel.org/r/20200708163929.2783-9-james.morse@arm.com