Correct the handling of edge cases for the VRECPS instruction:
 * this is a Neon instruction so uses the "standard FPSCR value"
 * (zero, inf) is a special case which returns 2.0

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>