xen/smp: Warn user why they keel over - nosmp or noapic and what to use instead.

xen/smp: Warn user why they keel over - nosmp or noapic and what to use instead.

commit ed467e69f16e6b480e2face7bc5963834d025f91 upstream.

We have hit a couple of customer bugs where they would like to
use those parameters to run an UP kernel - but both of those
options turn of important sources of interrupt information so
we end up not being able to boot. The correct way is to
pass in 'dom0_max_vcpus=1' on the Xen hypervisor line and
the kernel will patch itself to be a UP kernel.

Fixes bug: http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=637308

Acked-by: Ian Campbell <Ian.Campbell@eu.citrix.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>