aco: cleanup force-waitcnt output
If we don't reset ctx.vm_cnt/gpr_map/etc, this will spam a lot of s_waitcnt instructions.
image_sample_l v[4:6], v[20:23], s[16:23], s[12:15] dmask:0x7 dim:SQ_RSRC_IMG_CUBE ; f0900718 00640414
s_waitcnt vmcnt(0) lgkmcnt(0) ; bf8c0070
v_mov_b32_e32 v0, s5 ; 7e000205
s_waitcnt vmcnt(0) lgkmcnt(0) ; bf8c0070
v_fmamk_f32 v1, v14, 0x3f7fde30, v7 ; 58020f0e 3f7fde30
->
image_sample_l v[4:6], v[20:23], s[16:23], s[12:15] dmask:0x7 dim:SQ_RSRC_IMG_CUBE ; f0900718 00640414
s_waitcnt vmcnt(0) ; bf8c3f70
v_mov_b32_e32 v0, s5 ; 7e000205
v_fmamk_f32 v1, v14, 0x3f7fde30, v7 ; 58020f0e 3f7fde30