Hexagon (target/hexagon) Add v68 scalar instructions

Hexagon (target/hexagon) Add v68 scalar instructions

The following instructions are added
    L2_loadw_aq
    L4_loadd_aq
    R6_release_at_vi
    R6_release_st_vi
    S2_storew_rl_at_vi
    S4_stored_rl_at_vi
    S2_storew_rl_st_vi
    S4_stored_rl_st_vi

The release instructions are nop's in qemu.  The others behave as
 loads/stores.

The encodings for these instructions changed some "don't care" bits
    L2_loadw_locked
    L4_loadd_locked
    S2_storew_locked
    S4_stored_locked

Signed-off-by: Taylor Simpson <tsimpson@quicinc.com>
Reviewed-by: Anton Johansson <anjo@rev.ng>
Message-Id: <20230427224057.3766963-3-tsimpson@quicinc.com>