ARM: Expose vfp_get_fpscr() and vfp_set_fpscr() to C code

Expose the vfp_get_fpscr() and vfp_set_fpscr() functions to C
code as well as generated code, so we can use them to read and
write the FPSCR when saving and restoring VFP registers across
signal handlers in linux-user mode.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Riku Voipio <riku.voipio@nokia.com>
