SPARC was unconditionally setting CONFIG_SERIAL_CORE_CONSOLE to y
and conditionally setting CONFIG_SERIAL_CORE depending on the Sparc
sub-drivers.  In addition, the core serial driver for SPARC is
always built, so we end up with link errors.

We instead make CONFIG_SERIAL_CORE{,_CONSOLE} dependent on building
the SPARC core driver (CONFIG_SERIAL_SUNCORE).