[CompileTime] [Passes] Avoid computing unnecessary analyses. NFC

Similar to c515b2f3, If there are no loops in the function as seen
through LI, we should avoid computing the remaining expensive analyses
(such as SCEV, BPI).  Reordered the analyses requests and early return
if there are no loops.

The logic of avoiding expensive analyses is applied to LoopVectorizer,
LoopLoadElimination and LoopUnrollPass, i.e. all function passes which operate
on loops.

This is an NFC with compile time improvement.

Differential Revision: https://reviews.llvm.org/D124529