serial: 16550: Add Ingenic JZ4780 support

Add compatibility string for the Ingenic JZ4780 SoC, the necessary
UART enable bit into FCR and register shift. Neither are encoded
in the DTS coming from Linux, so we need to support it this way.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Tom Rini <trini@konsulko.com>
Cc: Simon Glass <sjg@chromium.org>
Cc: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
Cc: Paul Burton <paul.burton@imgtec.com>
Reviewed-by: Simon Glass <sjg@chromium.org>