Move the 'meta' dir to 'lib/cretonne/meta'.

The 'lib/cretonne' directory will be the new root of a stand-alone
cretonne crate containg both Python and Rust sources.

This is in preparation for publishing crates on crates.io.

lib/cretonne/meta/isa/riscv/defs.py

@@ -0,0 +1,14 @@
+"""
+RISC-V definitions.
+
+Commonly used definitions.
+"""
+from __future__ import absolute_import
+from cretonne import TargetISA, CPUMode
+import cretonne.base
+
+isa = TargetISA('riscv', [cretonne.base.instructions])
+
+# CPU modes for 32-bit and 64-bit operation.
+RV32 = CPUMode('RV32', isa)
+RV64 = CPUMode('RV64', isa)