pru-software-support: bump to latest version 5.7.0

pru-software-support: bump to latest version 5.7.0

Update to the latest version of the PRU software support [1].

There are minor changes to the license file mostly dates and versions --
notably pulling in several Linux kernel 5.4 header files in place of the
4.19 versions.  As there is no longer a dependency on the kernel types.h
  header, there's no longer a GPL-2.0 licensed component.

Also drop the useless comment that just repeats the URL.

[1] https://git.ti.com/cgit/pru-software-support-package/pru-software-support-package

Signed-off-by: Ash Charles <ashcharles@gmail.com>
[yann.morin.1998@free.fr: drop the URL-as-comment]
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>