target-arm: A64: Implement AdvSIMD reciprocal estimate insns URECPE, FRECPE

Implement URECPE and FRECPE instructions in both scalar and vector forms.
The actual reciprocal estimate function is shared with the A32/T32 Neon
code. However in A64 we aren't using the Neon "standard FPSCR value"
so extra checks are necessary to handle non-squashed denormal inputs
which can never happen for A32/T32. Calling conventions for the helpers
are thus modified to pass the fpst directly; we mark the helpers as
TCG_CALL_NO_RWG since we're changing the declarations anyway.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <rth@twiddle.net>
Message-id: 1394822294-14837-21-git-send-email-peter.maydell@linaro.org
