[intelxl] Increase data buffer size to 4kB

[intelxl] Increase data buffer size to 4kB

At least one E810 admin queue command (Query Default Scheduling Tree
Topology) insists upon being provided with a 4kB data buffer, even
when the data to be returned is much smaller.

Work around this requirement by increasing the admin queue data buffer
size to 4kB.

Signed-off-by: Michael Brown <mcb30@ipxe.org>