net: dsa: realtek: rtl8365mb: rename extport to extint

"extport" 0, 1, 2 was used to reference external ports id (ext0, ext1,
ext2). Meanwhile, port 0..9 is used as switch ports, including external
ports. "extport" was renamed to extint to make it clear it does not mean
the port number but the external interface number id.

The macros that map extint numbers to registers addresses now use inline
ifs instead of binary arithmetic.

Realtek uses in docs and drivers EXT_PORT0 (GMAC1) and EXT_PORT1
(GMAC2), with EXT_PORT0 being converted to ext_id == 1 and so on. It
might introduce some confusing while reading datasheets but it will not
be exposed to users.

"extint" was hardcoded to 1. However, some chips have multiple external
interfaces. It's not right to assume the CPU port uses extint 1 nor that
all extint are CPU ports. Now it came from a map between port number and
external interface id number.

This patch still does not allow multiple CPU ports nor extint as a non
CPU port.

Signed-off-by: Luiz Angelo Daros de Luca <luizluca@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>