akm8963: Make compilation of dummy library optional

For systems where the akm8963 library is present we don't want to
compile the dash dummy library.

Change-Id: If6b87696229edc6ae297f20e8003cc6207f18a55
Signed-off-by: Bjorn Andersson <bjorn.andersson@sonymobile.com>
bma250: Improve error prints

Make sure it's possible to distinguish between the different errors
appearing due to missing or incorrectly configured sysfs nodes.

Change-Id: I7350c2243c3f1a6be7b90bda22fc933dd307fc78
Signed-off-by: Bjorn Andersson <bjorn.andersson@sonymobile.com>