backport of patches to fix riscv build failure in 4.19-stable and 5.4-stable

Hi Greg,

The build of riscv allmodconfig fails in 4.19-stable and 5.4-stable.

4.19-stable will need: 30aca1bacb39 ("RISC-V: fix barrier() use in <vdso/processor.h>")

and 5.4-stable needs: 30aca1bacb39 ("RISC-V: fix barrier() use in <vdso/processor.h>") fc585d4a5cf6 ("riscv: Less inefficient gcc tishift helpers (and export their symbols)")

Backport of all are in the attached mbox.

-- Regards Sudip