[X86] Replace some if statements in isel address matching that should never be true...

[X86] Replace some if statements in isel address matching that should never be true with asserts. And move them earlier before we looked through operands that don't change size. NFC

These ifs were ensuring we don't have to handle types larger than 64 bits probably because we use getZExtValue in several places below them.

None of the callers of this code pass types larger than 64-bits so we can just assert instead of branching in release code.

I've also moved them earlier since we're just looking through operations that don't effect bit width.

This is prep work for some refactoring I plan to do to the (and (shl)) handling code.

llvm-svn: 358123