pseries: Increase default NVRAM size

pseries: Increase default NVRAM size

If no image file for NVRAM is specified, the pseries machine currently
creates a 16K non-persistent NVRAM by default.  This basically works, but
is not large enough for current firmware and guest kernels to create all
the NVRAM partitions they would like to.  Increasing the default size to
64K addresses this and stops the guest generating error messages.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Alexander Graf <agraf@suse.de>