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/UnitTests/Common/MathUtilTest.cpp

@@ -30,3 +30,11 @@ TEST(MathUtil, IntLog2)
   EXPECT_EQ(3, IntLog2(15));
   EXPECT_EQ(63, IntLog2(0xFFFFFFFFFFFFFFFFull));
 }
+
+TEST(MathUtil, NextPowerOf2)
+{
+  EXPECT_EQ(4, MathUtil::NextPowerOf2(3));
+  EXPECT_EQ(4, MathUtil::NextPowerOf2(4));
+  EXPECT_EQ(8, MathUtil::NextPowerOf2(6));
+  EXPECT_EQ(0x40000000, MathUtil::NextPowerOf2(0x23456789));
+}