parse: factor out mref parsing

parse: factor out mref parsing

Factor out the parsing of an mref from parse_line().  In order to
support the [base,index] syntax we need to be able to parse an mref in
two steps.

Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Signed-off-by: Jin Kyu Song <jin.kyu.song@intel.com>

• [DBH] parser.c