target-alpha: Fix fpcr_flush_to_zero initialization

The two bits required are UNDZ and UNFD, not UNDZ and DNOD.

Signed-off-by: Richard Henderson <rth@twiddle.net>
target-alpha: Remove DNOD bit from FPCR

It was never implemented, thus even for EV6 and EV7 the bit
is read-as-zero, writes-ignored.

Reported-by: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: Richard Henderson <rth@twiddle.net>