Move the SFP handling out of the common area into BANK3

sfp.c takes handle_sfp, sfp_module_read, sfp_apply_quirks, sfp_get_info,
sfp_read_field, sfp_print_info, setup_sfp_gpio, the quirk table and the module
state that goes with them. Everything exported is __banked: handle_sfp() and
sfp_print_info() are reached from cmd_parser.c in BANK2, the rest from the
common area, and both are bank boundaries.

The quirk table needed checking rather than assuming. Its entries are __code
pointers, and a __code pointer carries no bank, so passing one to a function in
a different bank hands it an offset read through the wrong window. That is safe
here because strcmp() sits in the common segment at 0x51f and is reached with a
plain lcall, so the bank register still says 3 while it runs. Verified in the
built image: the table at 0x35580 holds 0x563c and 0x5644, which resolve to
"QSFPTEK" and "QT-SFP+-T" inside BANK3.

Common segment 13393 -> 8432 bytes, leaving 7492 free rather than 2531. BANK3
holds 5710, BANK1 is unchanged and BANK2 grows by 31 for the trampolines.
All 34 machines in machine.h build and link, and the same walk over the
generated assembly finds no plain lcall crossing a bank boundary.

Makefile

@@ -60,6 +60,7 @@ SRCS = \
 	html_data.c \
 	rtlplayground.c \
 	boot.c \
+	sfp.c \
 	syslog.c \
 	udp_apps.c