hw/arm: Model TCMs in the SSE-300, not the AN547

The SSE-300 has an ITCM at 0x0000_0000 and a DTCM at 0x2000_0000.
Currently we model these in the AN547 board, but this is conceptually
wrong, because they are a part of the SSE-300 itself. Move the
modelling of the TCMs out of mps2-tz.c into sse300.c.

This has no guest-visible effects.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20210510190844.17799-7-peter.maydell@linaro.org