Make minimal updates to exisiting rules

1. logical left shift rules
a). add is_var_shift check for vslAA_immI rules.
b). for vslAA_reg rules, remove the matching for URShiftV cases as we
have the separate logical right shift rules now.

2. logical right shift rules
a). add vsrlAA_reg and vsrlAA_reg_var rules.
b). add is_var_shift check for vsrlAA_immI rules.

3. arithmetic right shift rules
a). add is_var_shift check for vsraAA_reg rules.
b). add vsraAA_reg_var rules
c). for vsraAA_immI rules, add is_var_shift check and update the match
primitive.

Code style issues(FIXME and the surrounding space in ins_pipe):
1. for modified rules, keep it as it was
2. for newly added rules, update the style

Author: shqking