cms-common: fix cmsarch for fc19_aarch64 cmsos

cmsos script returns fc19_aarch64 or fc19_armv7hl, yet cmsarch
script expected an additional underscore after cmsos. Resolve it
by checking exact match to cmsos.

Signed-off-by: David Abdurachmanov <David.Abdurachmanov@cern.ch>
Merge pull request #935 from davidlt/fix-cms-common-aarch64

cms-common: fix cmsarch for fc19_aarch64 cmsos