net: dsa: rtl8366rb: Fix compilation problem

net: dsa: rtl8366rb: Fix compilation problem

When the kernel is compiled without LED framework support the
rtl8366rb fails to build like this:

rtl8366rb.o: in function `rtl8366rb_setup_led':
rtl8366rb.c:953:(.text.unlikely.rtl8366rb_setup_led+0xe8):
  undefined reference to `led_init_default_state_get'
rtl8366rb.c:980:(.text.unlikely.rtl8366rb_setup_led+0x240):
  undefined reference to `devm_led_classdev_register_ext'

As this is constantly coming up in different randconfig builds,
bite the bullet and create a separate file for the offending
code, split out a header with all stuff needed both in the
core driver and the leds code.

Add a new bool Kconfig option for the LED compile target, such
that it depends on LEDS_CLASS=y || LEDS_CLASS=RTL8366RB
which make LED support always available when LEDS_CLASS is
compiled into the kernel and enforce that if the LEDS_CLASS
is a module, then the RTL8366RB driver needs to be a module
as well so that modprobe can resolve the dependencies.

Fixes: 32d617005475 ("net: dsa: realtek: add LED drivers for rtl8366rb")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202502070525.xMUImayb-lkp@intel.com/
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>