[ARM] check bitwidth in PerformORCombine

When simplifying a (or (and B A) (and C ~A)) to a (VBSL A B C) ensure that the
bitwidth of the second operands to both ands match before comparing the negation
of the values.

Split the check of the value of the second operands to the ands.  Move the cast
and variable declaration slightly higher to make it slightly easier to follow.

Bug-Id: 16700
Signed-off-by: Saleem Abdulrasool <compnerd@compnerd.org>