Faster blitting @ BB8/BBRGB32 when no processing is needed (#4847)

* Pickup the eponymous blitting performance tweaks from koreader/koreader-base#878
* Cleanup BitOpts usage (require & cache)
* Unify oddness checks (MOD -> AND)
* Enforce the native Portrait orientation on Kobo (except @ 16bpp, i.e., KSM w/ 8bpp swap disabled), to allow for faster blitting when unrotted.
* Switch CRe BB to 32BPP on color screens
* Minor cleanups

frontend/optmath.lua

@@ -2,8 +2,12 @@
 Simple math helper functions
 ]]
 
+local bit = require("bit")
+
 local Math = {}
 
+local band = bit.band
+
 function Math.roundAwayFromZero(num)
     if num > 0 then
         return math.ceil(num)
@@ -17,7 +21,7 @@ function Math.round(num)
 end
 
 function Math.oddEven(number)
-    if number % 2 == 1 then
+    if band(number, 1) == 1 then
         return "odd"
     else
         return "even"