Rename Log2 and add IsPow2 to MathUtils for future use

Also remove unused pow2/pow2f functions.

Source/Core/VideoBackends/OGL/StreamBuffer.cpp

@@ -23,7 +23,7 @@ static u32 genBuffer()
 }
 
 StreamBuffer::StreamBuffer(u32 type, u32 size)
-: m_buffer(genBuffer()), m_buffertype(type), m_size(ROUND_UP_POW2(size)), m_bit_per_slot(Log2(ROUND_UP_POW2(size) / SYNC_POINTS))
+: m_buffer(genBuffer()), m_buffertype(type), m_size(ROUND_UP_POW2(size)), m_bit_per_slot(IntLog2(ROUND_UP_POW2(size) / SYNC_POINTS))
 {
 	m_iterator = 0;
 	m_used_iterator = 0;