Avoid SkFixed overflow in decal bitmap procs

Avoid SkFixed overflow in decal bitmap procs

The check for decal mode can overflow in SkFixed.  Promote to
64bit (48.16) instead.

Also update can_truncate_to_fixed_for_decal() to take SkFixed params and
used it in ClampX_ClampY_filter_scale_SSE2().

BUG=chromium:675444
R=reed@google.com

CQ_INCLUDE_TRYBOTS=skia.primary:Test-Ubuntu-GCC-GCE-CPU-AVX2-x86_64-Release-SKNX_NO_SIMD

Change-Id: I759464cdaa5c005159e38e32167fb1937e2a1d28
Reviewed-on: https://skia-review.googlesource.com/6538
Reviewed-by: Cary Clark <caryclark@google.com>
Commit-Queue: Florin Malita <fmalita@chromium.org>