pgsql: Modify additional power 2 calculations to use new helper functio

Modify additional power 2 calculations to use new helper functions

2nd pass of modifying various places which obtain the next power
of 2 of a number and make them use the new functions added in
f0705bb62.

In passing, also modify num_combinations(). This can be implemented
using simple bitshifting rather than looping.

Reviewed-by: John Naylor
Discussion: https://postgr.es/m/20200114173553.GE32763%40fetter.org

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/02a2e8b442002a698336954633b0ccc4e30061e6

Modified Files
--------------
src/backend/access/gin/ginfast.c    | 12 +++---------
src/backend/executor/nodeHash.c     |  8 ++------
src/backend/nodes/list.c            | 15 +++++++--------
src/backend/statistics/mvdistinct.c | 10 +---------
src/backend/utils/adt/arrayfuncs.c  |  9 +++------
5 files changed, 16 insertions(+), 38 deletions(-)