libxc: add xc_hvm_param_get/set() to get/set 64-bit values

libxc: add xc_hvm_param_get/set() to get/set 64-bit values

HVMOP_get_param and HVMOP_set_param take a uint32_t for the parameter
index and a uint64_t for the value.  So add xc_hvm_param_get() and
xc_hvm_param_set() that take the same types.

The existing xc_get_hvm_param() and xc_set_hvm_param() are retained
for compatibility but are deprecated.

Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
[ ijc -- dropped one hunk against xen-access.c which didn't apply due to
         intervening changes ]