Switch from xc_{set,get}_hvm_param to xc_hvm_param_{set,get}

Switch from xc_{set,get}_hvm_param to xc_hvm_param_{set,get}

The former have been deprecated for some time (they take unsigned
longs, not uint64_t's, and therefore risk truncation for some params)
and I'm about to remove them.

Since _get takes a uint64_t * for the output instead of an unsigned
long * it is necessary to change the types of a few variables. I
checked each case would be OK with it and either the variable is
already downcast (to something like a uint32_t) when it is
subsequently used or it was used as a wider type already (so this
change might resolve a latent bug under some circumstances?).

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>