[AMDGPU][MC][DOC] Updated AMD GPU assembler description

Stage 2: added detailed description of operands

See bug 36572: https://bugs.llvm.org/show_bug.cgi?id=36572

llvm-svn: 349368
diff --git a/llvm/docs/AMDGPU/gfx8_base_smem_addr.rst b/llvm/docs/AMDGPU/gfx8_base_smem_addr.rst
new file mode 100644
index 0000000..81ef255
--- /dev/null
+++ b/llvm/docs/AMDGPU/gfx8_base_smem_addr.rst
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+..
+    **************************************************
+    *                                                *
+    *   Automatically generated file, do not edit!   *
+    *                                                *
+    **************************************************
+
+.. _amdgpu_synid8_base_smem_addr:
+
+sbase
+===========================
+
+A 64-bit base address for scalar memory operations.
+
+*Size:* 2 dwords.
+
+*Operands:* :ref:`s<amdgpu_synid_s>`, :ref:`flat_scratch<amdgpu_synid_flat_scratch>`, :ref:`xnack<amdgpu_synid_xnack>`, :ref:`vcc<amdgpu_synid_vcc>`, :ref:`trap<amdgpu_synid_trap>`