CA-118880: backport "xen/hvc: allow xenboot console to be used again"

Backport a9fbf4d591da6cd1d3eaab826c7c15f77fc8f6a3 from upstream so
earlyprintk=xen can be used to investigate early boot crashes in the
kernel.
CA-118880: Set CONFIG_NR_CPUS=8 to fix a h/w specific boot failure

dottyback, a 16 PCPU intel box fails to boot with a "Max apic_id
exceeded!" panic if NR_CPUS=15, but is fine with NR_CPUS=8.
Eric's net-device allocation improvement patch
Revert "Revert "Update netback to net tip (27/09/2013)""

This reverts commit 9288d8c19bac99d33c1b45720a1e49e57bf49573.