x86: increment default page pool pages

With the current identity mapping scheme a new test requires
some more memory to be set aside here.

In production this parameter gets turned per-board, and
the pending paging code overhaul in #27001 significantly
relaxes this as driver I/O mappings are no longer sparse.

Fixes a runtime failure in tests/kernel/device on
qemu_x86_64 that somehow slipped past CI.

Signed-off-by: Andrew Boie <andrew.p.boie@intel.com>