[NFCI] Ensure TargetOpcode::* are compatible with guessInstructionProperties=0

rL162640 introduced CodeGenTarget::guessInstructionProperties. If a target 
sets guessInstructionProperties=0 in its FooInstrInfo, tablegen will error if 
it has to guess properties from patterns. Unfortunately, 
guessInstructionProperties=0 can't be used with current upstream LLVM as 
instructions in the TargetOpcode namespace are always included and sometimes 
have inferred properties for mayLoad, mayStore, and hasSideEffects. This patch 
provides the simplest possible fix to this problem, setting default values for 
these fields in the TargetOpcode scope. There is no intended functional 
change, as the explicitly set properties should match what was previously 
inferred. A number of the instructions had hasSideEffects=1 inferred 
unintentionally. This patch makes it explicit, while future patches (such as 
D37097) correct the property.

Differential Revision: https://reviews.llvm.org/D37065

llvm-svn: 317674