MAINTAINERS: update sound/soc/intel maintainers

The information for Intel SoC drivers was not updated for several
years. Add myself, Liam and Keyon (Jie) as maintainers to get notified
of contributions and bug reports. As discussed with Mark and Takashi,
I'll also monitor alsa-devel and ack Intel patches as necessary.

Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>