A handful of the scalar crypto instructions are supposed to take a 
constant integer argument 0..3 inclusive.  A suitable constraint was 
created and used for this purpose (D03), but the operand's predicate is 
"register_operand".  That's just wrong.

This patch adds a new predicate "const_0_3_operand" and fixes the 
relevant insns to use it.  One could argue the constraint is redundant 
now (and you'd be correct).  I wouldn't lose sleep if someone wanted 
that removed, in which case I'll spin up a V2.

The testsuite was broken in a way that made it consistent with the 
compiler, so the tests passed, when they really should have been issuing 
errors all along.

This patch adjusts the existing tests so that they all expect a 
diagnostic on the invalid operand usage (including out of range 
constants).  It adds new tests with proper constants, testing the 
extremes of valid values.

OK for the trunk, or should we remove the D03 constraint?

Jeff