[X86] Remove special validation for INT immediate operand from AsmParser. Instead mark its operand type as u8imm which will cause it to fail to match. This is more consistent with other instruction behavior.

This also fixes a bug where negative immediates below -128 were not being reported as errors.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@249989 91177308-0d34-0410-b5e6-96231b3b80d8
5 files changed