lib/codegen-meta moved into lib/codegen. (#423)

* lib/codegen-meta moved into lib/codegen.

* Renamed codegen-meta and existing meta.

lib/codegen/meta-python/isa/riscv/registers.py

@@ -0,0 +1,23 @@
+"""
+RISC-V register banks.
+"""
+from __future__ import absolute_import
+from cdsl.registers import RegBank, RegClass
+from .defs import ISA
+
+
+# We include `x0`, a.k.a `zero` in the register bank. It will be reserved.
+IntRegs = RegBank(
+        'IntRegs', ISA,
+        'General purpose registers',
+        units=32, prefix='x')
+
+FloatRegs = RegBank(
+        'FloatRegs', ISA,
+        'Floating point registers',
+        units=32, prefix='f')
+
+GPR = RegClass(IntRegs)
+FPR = RegClass(FloatRegs)
+
+RegClass.extract_names(globals())