serial: earlycon: Show the earlycon "driver" in banner

Output the earlycon "driver" from the just-parsed console 'name'
and 'index' fields.

NB: ->mapbase is a resource_size_t so use %pa format specifier

Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>