[GlobalISel][X86] Support G_LSHR/G_ASHR/G_SHL

[GlobalISel][X86] Support G_LSHR/G_ASHR/G_SHL

Support G_LSHR/G_ASHR/G_SHL. We have 3 variance for
shift instructions : shift gpr, shift imm, shift 1.
Currently GlobalIsel TableGen generate patterns for
shift imm and shift 1, but with shiftCount i8.
In G_LSHR/G_ASHR/G_SHL like LLVM-IR both arguments
has the same type, so for now only shift i8 can use
auto generated TableGen patterns.

The support of G_SHL/G_ASHR enables tryCombineSExt
from LegalizationArtifactCombiner.h to hit, which
results in different legalization for the following tests:
    LLVM :: CodeGen/X86/GlobalISel/ext-x86-64.ll
    LLVM :: CodeGen/X86/GlobalISel/gep.ll
    LLVM :: CodeGen/X86/GlobalISel/legalize-ext-x86-64.mir

-; X64-NEXT:    movsbl %dil, %eax
+; X64-NEXT:    movl $24, %ecx
+; X64-NEXT:    # kill: def $cl killed $ecx
+; X64-NEXT:    shll %cl, %edi
+; X64-NEXT:    movl $24, %ecx
+; X64-NEXT:    # kill: def $cl killed $ecx
+; X64-NEXT:    sarl %cl, %edi
+; X64-NEXT:    movl %edi, %eax

..which is not optimal and should be addressed later.

Rework of the patch by igorb

Reviewed By: igorb

Differential Revision: https://reviews.llvm.org/D44395

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@327499 91177308-0d34-0410-b5e6-96231b3b80d8