x86/hvm: Improve memory_op hypercall dispatching

x86/hvm: Improve memory_op hypercall dispatching

hvm_memory_op() and hvm_memory_op_compat32() are almost identical, but there
is no need to have two functions instantiated at the end of different function
pointers.

Combine the two into single hvm_memory_op() which dispatches to
{do,compat}_memory_op() based on the hcall_64bit setting.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Wei Liu <wei.liu2@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>