arch: mips: fix unmet dependency for DEBUG_INFO

When SB1XXX_CORELIS is enabled, COMPILE_TEST is disabled,
and DEBUG_KERNEL is disabled, Kbuild gives the
following warning:

WARNING: unmet direct dependencies detected for DEBUG_INFO
  Depends on [n]: DEBUG_KERNEL [=n] && !COMPILE_TEST [=n]
  Selected by [y]:
  - SB1XXX_CORELIS [=y] && SIBYTE_SB1xxx_SOC [=y] && !COMPILE_TEST [=n]

This is because SB1XXX_CORELIS selects DEBUG_INFO without
selecting or depending on DEBUG_KERNEL, despite DEBUG_INFO
depending on DEBUG_KERNEL.

Signed-off-by: Julian Braha <julianbraha@gmail.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>