serial: 8250: move mmp|pxa uart earlycon code

serial: 8250: move mmp|pxa uart earlycon code

There are two other drivers that bind to "mrvl,mmp-uart": the 8250_of
and the 8250_pxa. The previous one is generic and the latter is binded
to ARCH_PXA || ARCH_MMP. Now we may have pxa programming compatible
HW to support, making use of the generic 8250_of seems a good idea.
However, there's no earlycon support if we go with this solution. So
move the mmp|pxa-uart earlycon code to core 8250_early.c.

Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
Link: https://lore.kernel.org/r/20240711160720.3488-2-jszhang@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>