[CORE] net: Refurbish netswitch software bridge

The software bridge is our default netswitch policy that is
always compiled with our core packet switching framework.

This patch does cleanups and simplifies the software bridge
implementation so that its more readable and easy to maintain.

Signed-off-by: Anup Patel <anup@brainfault.org>
[ARM] Rename default bridge instance to br0

All supported ARM host have DTS files creating a default vmm_netswitch
named "netbridge0" which is nothing but a software bridge.

In Linux world, software bridges are typically named "br0", "br1"
and so on.

For easy in understanding, we will name vmm_netswitch instances with
software bridge policy as "br0", "br1", and so on.

As per above rationale, we rename "netbridge0" to "br0" in DTS files of
various ARM hosts.

Signed-off-by: Anup Patel <anup@brainfault.org>
Merge remote-tracking branch 'upstream/master' into x86-next
[x86] Move generic pagetable code in seperate file.

Since the same page table maintenance code can be shared
between host and nested page table management, move the
common code in a different file.

Signed-off-by: Himanshu Chauhan <hschauhan@nulltrace.org>