lib: bitrev: Sync with Linux kernel v4.17

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

SPDX: Convert all of our single license tags to Linux Kernel style

When U-Boot started using SPDX tags we were among the early adopters and
there weren't a lot of other examples to borrow from. So we picked the
area of the file that usually had a full license text and replaced it
with an appropriate SPDX-License-Identifier: entry. Since then, the
Linux Kernel has adopted SPDX tags and they place it as the very first
line in a file (except where shebangs are used, then it's second line)
and with slightly different comment styles than us.

In part due to community overlap, in part due to better tag visibility
and in part for other minor reasons, switch over to that style.

This commit changes all instances where we have a single declared
license in the tag as both the before and after are identical in tag
contents. There's also a few places where I found we did not have a tag
and have introduced one.

Signed-off-by: Tom Rini <trini@konsulko.com>

Add GPL-2.0+ SPDX-License-Identifier to source files

Signed-off-by: Wolfgang Denk <wd@denx.de>
[trini: Fixup common/cmd_io.c]
Signed-off-by: Tom Rini <trini@ti.com>

lib: import bitrev library from the linux kernel

This patch adds the bitrev library from the linux kernel. This is a simple
algorithm that uses an 8 bit look-up table to reverse the bits in data types of
8, 16, or 32 bit widths. The docg4 nand flash driver uses it.

[port from linux kernel v3.9 commit 7ee32a6d30d1c8a3b7a07a6269da8f0a08662927]
[originally added: v2.6.20 by commit a5cfc1ec58a07074dacb6aa8c79eff864c966d12]

Signed-off-by: Mike Dunn <mikedunn@newsguy.com>