CommonFuncs: Convert ROUND_UP_POW2 macro to a function

Also move it to MathUtils where it belongs with the rest of the
power-of-two functions. This gets rid of pollution of the current scope
of any translation unit with b<value> macros that aren't intended to be
used directly.

Source/Core/Common/MathUtil.h

@@ -29,6 +29,19 @@ constexpr bool IsPow2(T imm)
   return imm > 0 && (imm & (imm - 1)) == 0;
 }
 
+constexpr u32 NextPowerOf2(u32 value)
+{
+  --value;
+  value |= value >> 1;
+  value |= value >> 2;
+  value |= value >> 4;
+  value |= value >> 8;
+  value |= value >> 16;
+  ++value;
+
+  return value;
+}
+
 template <class T>
 struct Rectangle
 {