hw/arm/mps2-tz: Correct the OSCCLK settings for mps2-an505 and mps2-an511

We were previously using the default OSCCLK settings, which are
correct for the older MPS2 boards (mps2-an385, mps2-an386,
mps2-an500, mps2-an511), but wrong for the mps2-an505 and mps2-511
implemented in mps2-tz.c.  Now we're setting the values explicitly we
can fix them to be correct.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20210215115138.20465-4-peter.maydell@linaro.org