haven: Clean up payload sizes

VMID is represented inconsistently in payload structs. Consistently use
hh_vmid_t to reduce mistakes around sizing of vmid. IRQ notify request
payload was also incorrectly formatted according to specification.

Change-Id: I0875655f69946eb0af609c67bdfdfa0dab5c7acc
Signed-off-by: Elliot Berman <eberman@codeaurora.org>