target/arm: Handle floating point registers in exception entry

target/arm: Handle floating point registers in exception entry

Handle floating point registers in exception entry.
This corresponds to the FP-specific parts of the pseudocode
functions ActivateException() and PushStack().

We defer the code corresponding to UpdateFPCCR() to a later patch.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20190416125744.27770-11-peter.maydell@linaro.org