{hyper,multi}call: further limit arguments to just 5

{hyper,multi}call: further limit arguments to just 5

Multicall compat translation and hypercall continuation handling can
also be shrunk to the processing of just (up to) 5 arguments.

Take the opportunity to
- make exceeding the limit noisy in hypercall_create_continuation(),
- use speculation-safe array access in hypercall_create_continuation(),
- avoid a Misra C:2012 Rule 19.1 violation in xlat_multicall_entry(),
- further tidy xlat_multicall_entry() and __trace_multicall_call()
  style-wise.

Amends: 2f531c122e95 ("x86: limit number of hypercall parameters to 5")
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Stefano Stabellini <sstabellini@kernel.org> # arm