mtd: rawnand: denali: use SPDX-License-Identifier and fix license mismatch

mtd: rawnand: denali: use SPDX-License-Identifier and fix license mismatch

Use SPDX-License-Identifier instead of the license boilerplates.

This conversion makes it easier for us to scan the license, then
I notice license mismatch problems.

The license blocks in denali* indicate GPL-2.0 "only", while the
MODULE_LICENSE in denali.c and denali_dt.c is GPL-2.0 "or later"
as explained in include/linux/module.h as follows:

  "GPL"                           [GNU Public License v2 or later]
  "GPL v2"                        [GNU Public License v2]

I fixed the MODULE_LICENSE tags, assuming the license blocks are
the authors' intention.

Also, add missing MODULE_DESCRIPTION/AUTHOR to denali.c

While I am touching the license things, I added my credit to denali.c
because this driver was largely re-written by me in 2017.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>