target/sparc: Merge advance_jump_uncond_{never,always} into advance_jump_cond

Handle these via TCG_COND_{ALWAYS,NEVER}.
Allow dc->npc to be variable, using gen_mov_pc_npc.

Tested-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Acked-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>