linux-user/sparc: Handle tstate in sparc64_get/set_context()

linux-user/sparc: Handle tstate in sparc64_get/set_context()

Correctly implement save/restore of the tstate field in
sparc64_get_context() and sparc64_set_context():
 * Don't use the CWP value from the guest in set_context
 * Construct and save a tstate value rather than leaving
   it as zero in get_context

To do this we factor out the "calculate TSTATE value from CPU state"
code from sparc_cpu_do_interrupt() into its own sparc64_tstate()
function; that in turn requires us to move some of the function
prototypes out from inside a CPU_NO_IO_DEFS ifdef guard.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20201106152738.26026-5-peter.maydell@linaro.org>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>