goarch: Add riscv64

Although RISC-V 64-bit doesn't have official golang support there are
forks that now exist with at least some support and work is ongoing in
the upstream tree. In order to be able to use the goarch class add
support for RISC-V.

For more details see here:
golang/go#27532

Signed-off-by: Alistair Francis <[email protected]>
Signed-off-by: Richard Purdie <[email protected]>

Author: alistair23

meta/classes/goarch.bbclass

@@ -68,6 +68,8 @@ def go_map_arch(a, d):
         return 'ppc64'
     elif re.match('p(pc|owerpc)(64el)', a):
         return 'ppc64le'
+    elif a == 'riscv64':
+        return 'riscv64'
     else:
         raise bb.parse.SkipRecipe("Unsupported CPU architecture: %s" % a)