Add additional pages to the guest to account for the number of pages
the ucall headers need.  The only reason things worked before is the
ucall headers are fairly small.  If they were ever to increase in
size the guest could run out of memory.

This is done in preparation for adding string formatting options to
the guest through the ucall framework which increases the size of
the ucall headers.

Fixes: 426729b2 ("KVM: selftests: Add ucall pool based implementation")
Signed-off-by: Aaron Lewis <aaronlewis@google.com>
Link: https://lore.kernel.org/r/20230729003643.1053367-7-seanjc@google.comSigned-off-by: Sean Christopherson <seanjc@google.com>