Clean up nbnxm bounding box functions

Clean up nbnxm bounding box functions

Replaced macro function by inline function.
Reduced and simplified function arguments.
Renamed functions with more expressive names.
Removed _simd4 from the SIMD4 version of the normal BB distance
calculation function, since it can be used everywhere and this
reduced preprocessing logic.
Replaced nbnxn_bb_t by BoundingBox.

Change-Id: I63a7a0add371b268b533bde60e15a644ec71583e