hv:move some common APIs to io_req.c

Now the io_emul.c is relates with arch,io_req.c is common,
move some APIs from io_emul.c to io_req.c as common like these APIs:
register_pio/mmio_emulation_handler
dm_emulate_pio/mmio_complete
pio_default_read/write
mmio_default_access_handler
hv_emulate_pio/mmio etc

Tracked-On: #1842
Signed-off-by: Mingqiang Chi <mingqiang.chi@intel.com>
Reviewed-by: Jason Chen CJ <jason.cj.chen@intel.com>
Acked-by: Eddie Dong <eddie.dong@intel.com>

Author: mingqiangchi