via-rng: enable secondary noise source on CPUs where it is present

via-rng: enable secondary noise source on CPUs where it is present

In the padlock spec:

"SRC Bits[9:8] Noise source select (I): These bits control the two noise
 sources on the processor that input bits to the accumulation buffers.
 On Nehemiah processors prior to stepping 8, these bits are reserved
 and undefined. The default RESET state is both bits = 0."

Signed-off-by: Dave Jones <[email protected]>
Tested-by: Udo van den Heuvel <[email protected]>
Cc: Michael Buesch <[email protected]>
Cc: folkert van Heusden <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>