x86/HVM: fix hvmemul_rep_outs_set_context()

x86/HVM: fix hvmemul_rep_outs_set_context()

There were two issues with this function: Its use of
hvmemul_do_pio_buffer() was wrong (the function deals only with
individual port accesses, not repeated ones, i.e. passing it
"*reps * bytes_per_rep" does not have the intended effect). And it
could have processed a larger set of operations in one go than was
probably intended (limited just by the size that xmalloc() can hand
back).

By converting to proper use of hvmemul_do_pio_buffer(), no intermediate
buffer is needed at all. As a result a preemption check is being added.

Also drop unused parameters from the function.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Razvan Cojocaru <rcojocaru@bitdefender.com>
Reviewed-by: Paul Durrant <paul.durrant@citrix.com>