remove set_fs for riscv v2

[Christoph Hellwig]

Hi all,

this series converts riscv to the new set_fs less world and is on top of this
branch:

    https://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs.git/log/?h=base.set_fs

The first four patches are general improvements and enablement for all nommu
ports, and might make sense to merge through the above base branch.

Changes since v1:
 - implement __get_user_fn and __put_user_fn for the UACCESS_MEMCPY case
   and remove the small constant size optimizations in raw_copy_from_user
   and raw_copy_to_user
 - reshuffle the patch order a little

Diffstat
 arch/riscv/Kconfig                   |    2 
 arch/riscv/include/asm/thread_info.h |    6 -
 arch/riscv/include/asm/uaccess.h     |  177 +++++++++++++++++------------------
 arch/riscv/kernel/process.c          |    1 
 arch/riscv/lib/Makefile              |    2 
 include/asm-generic/uaccess.h        |  109 +++++++++++++--------
 include/linux/uaccess.h              |    4 
 7 files changed, 166 insertions(+), 135 deletions(-)