Documentation: dt: mtd: replace "nor-jedec" binding with "jedec, spi-nor"

In commit 8ff16cf7 ("Documentation: devicetree: m25p80: add "nor-jedec"
binding"), we added a generic "nor-jedec" binding to catch all
mostly-compatible SPI NOR flash which can be detected via the READ ID
opcode (0x9F). This was discussed and reviewed at the time, however
objections have come up since then as part of this discussion:

  http://lkml.kernel.org/g/20150511224646.GJ32500@ld-irv-0074



It seems the parties involved agree that "jedec,spi-nor" does a better
job of capturing the fact that this is SPI-specific, not just any NOR
flash.

This binding was only merged for v4.1-rc1, so it's still OK to change
the naming.

At the same time, let's move the documentation to a better name.

Next up: stop referring to code (drivers/mtd/devices/m25p80.c) from the
documentation.

Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Cc: Marek Vasut <marex@denx.de>
Cc: Rafał Miłecki <zajec5@gmail.com>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Pawel Moll <pawel.moll@arm.com>
Cc: Ian Campbell <ijc+devicetree@hellion.org.uk>
Cc: Kumar Gala <galak@codeaurora.org>
Cc: devicetree@vger.kernel.org
Acked-by: Stephen Warren <swarren@nvidia.com>
Acked-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Mark Rutland <mark.rutland@arm.com>