[AVR] Add the assembly instruction printer

Summary:
This change adds the AVR assembly instruction printer.

No tests are included in this patch. I have left them downstream so we can
add them once `llc` successfully runs (there's very few components left
to upstream until this).

Reviewers: arsenm, kparzysz

Subscribers: wdng, beanz, mgorny

Differential Revision: https://reviews.llvm.org/D25028

llvm-svn: 282854
diff --git a/llvm/lib/Target/AVR/LLVMBuild.txt b/llvm/lib/Target/AVR/LLVMBuild.txt
index c987886..c7f5bd1 100644
--- a/llvm/lib/Target/AVR/LLVMBuild.txt
+++ b/llvm/lib/Target/AVR/LLVMBuild.txt
@@ -22,7 +22,7 @@
 type = TargetGroup
 name = AVR
 parent = Target
-has_asmprinter = 0
+has_asmprinter = 1
 has_asmparser = 1
 
 [component_1]