make enabling LOWP stages simpler

This method is a little simpler macro-wise,
and makes it easier to guard new lowp stages:

  LOWP(foo)
  LOWP(bar)
  #ifndef SK_LEGACY_LOWP_BAZ
    LOWP(baz)
  #endif

Change-Id: I06392f5cf7a04651e7bf47e79f10f7da8520f5ab
Reviewed-on: https://skia-review.googlesource.com/63141
Reviewed-by: Florin Malita <fmalita@chromium.org>
Commit-Queue: Mike Klein <mtklein@chromium.org>
1 file changed