MAINTAINERS: add hvc_console

Add a MAINTAINERS entry for the hypervisor virtual console driver.

Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Acked-by: Josh Boyer <jwboyer@linux.vnet.ibm.com>
Cc: Josh Boyer <jwboyer@linux.vnet.ibm.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>