Revert "X86 platform: New BayTrail IOSF-SB MBI driver"

This reverts commit 997ab407. This driver is
replaced by the more general SOC IOSF driver in commit 46184415.

Signed-off-by: David E. Box <david.e.box@linux.intel.com>
Signed-off-by: Matthew Garrett <matthew.garrett@nebula.com>