serial: 8250_early: Add earlycon support for Palmchip UART

Define an OF early console for Palmchip UART, which can be enabled
by passing "earlycon" on the boot command line.

Signed-off-by: Marc Gonzalez <marc_gonzalez@sigmadesigns.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>