FROMLIST: hvc_dcc: bind driver to core0 for reads and writes

Some debuggers, such as Trace32 from Lauterbach GmbH, do not handle
reads/writes from/to DCC on secondary cores.  Each core has its
own DCC device registers, so when a core reads or writes from/to DCC,
it only accesses its own DCC device.  Since kernel code can run on
any core, every time the kernel wants to write to the console, it
might write to a different DCC.

In SMP mode, Trace32 only uses the DCC on core 0.  In AMP mode, it
creates multiple windows, and each window shows the DCC output
only from that core's DCC.  The result is that console output is
either lost or scattered across windows.

Selecting this option will enable code that serializes all console
input and output to core 0.  The DCC driver will create input and
output FIFOs that all cores will use.  Reads and writes from/to DCC
are handled by a workqueue that runs only core 0.

Bug: 169129589
Link: https://lore.kernel.org/lkml/1435344756-20901-1-git-send-email-timur@codeaurora.org/


Signed-off-by: Shanker Donthineni <shankerd@codeaurora.org>
Acked-by: Adam Wallis <awallis@codeaurora.org>
Signed-off-by: Timur Tabi <timur@codeaurora.org>
[eberman@codeaurora.org: Resolve trivial merge conflicts]
Signed-off-by: Elliot Berman <eberman@codeaurora.org>
Change-Id: Ie5e3f25ad74a0f07edb862b8258ad875ea308d30