dt-bindings: Use 'enum' instead of 'oneOf' plus 'const' entries

'enum' is equivalent to 'oneOf' with a list of 'const' entries, but 'enum'
is more concise and yields better error messages.

Cc: Maxime Ripard <mripard@kernel.org>
Cc: Vignesh R <vigneshr@ti.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
Cc: Lee Jones <lee.jones@linaro.org>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: Kishon Vijay Abraham I <kishon@ti.com>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: dmaengine@vger.kernel.org
Cc: linux-i2c@vger.kernel.org
Cc: linux-media@vger.kernel.org
Cc: netdev@vger.kernel.org
Cc: linux-pci@vger.kernel.org
Cc: linux-phy@lists.infradead.org
Cc: linux-serial@vger.kernel.org
Cc: alsa-devel@alsa-project.org
Cc: linux-spi@vger.kernel.org
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com> (mipi-ccs)
Acked-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Vinod Koul <vkoul@kernel.org>
Acked-By: Vinod Koul <vkoul@kernel.org>
Acked-by: Wolfram Sang <wsa@kernel.org> # for I2C
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20210824202014.978922-1-robh@kernel.org