s390x: Exploit LOCGHI for converting from CC to Int1

s390x: Exploit LOCGHI for converting from CC to Int1

Whenever converting a condition code to a Boolean value, the current
implementation in s390_insn_cc2bool_emit() generates six instructions
including "insert program mask" (IPM).  On systems with the
load/store-on-condition facility 2, this can be done in two instructions
instead, using "load halfword immediate on condition" (LOCGHI).

Add the new hardware capability VEX_HWCAPS_S390X_LSC2 and the respective
macro s390_host_has_lsc2.  In s390_insn_cc2bool_emit(), check for the
facility and exploit it if available.

A conditional move from an immediate value can be slightly improved with
LOCGHI as well, so do that in s390_insn_cond_move_emit() if possible.