csky: Add C based string functions

Try to access RAM with the largest bit width possible, but without
doing unaligned accesses.

A further improvement could be to use multiple read and writes as the
assembly version was trying to do.

Tested on a BeagleV Starlight with a SiFive U74 core, where the
improvement is noticeable.

Signed-off-by: Matteo Croce <mcroce@microsoft.com>
Co-developed-by: Guo Ren <guoren@linux.alibaba.com>
Signed-off-by: Guo Ren <guoren@linux.alibaba.com>

csky: Fixup abiv1 memset error

Current memset implementation in abiv1 is wrong and it'll cause unalign
access. Just remove it and use the generic one. This patch will cause
performance degradation and we will improve it with a new design in next
patchset.

Signed-off-by: Guo Ren <ren_guo@c-sky.com>
Cc: Arnd Bergmann <arnd@arndb.de>

treewide: Add SPDX license identifier - Makefile/Kconfig

Add SPDX license identifiers to all Make/Kconfig files which:

- Have no license information of any form

These files fall under the project license, GPL v2 only. The resulting SPDX
license identifier is:

GPL-2.0-only

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

csky: Build infrastructure

This patch adds Makefile, Kconfig for build infrastructure.

Signed-off-by: Guo Ren <ren_guo@c-sky.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>