mfd/syscon: Add device_node_to_regmap()

device_node_to_regmap() is exactly like syscon_node_to_regmap(), but it
does not check that the node is compatible with "syscon", and won't
attach the first clock it finds to the regmap.

The rationale behind this, is that one device node with a standard
compatible string "foo,bar" can be covered by multiple drivers sharing a
regmap, or by a single driver doing all the job without a regmap, but
these are implementation details which shouldn't reflect on the
devicetree.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: James Hogan <jhogan@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Lee Jones <lee.jones@linaro.org>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Michael Turquette <mturquette@baylibre.com>
Cc: Stephen Boyd <sboyd@kernel.org>
Cc: Jason Cooper <jason@lakedaemon.net>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: devicetree@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: linux-doc@vger.kernel.org
Cc: linux-mips@vger.kernel.org
Cc: linux-clk@vger.kernel.org
Cc: od@zcrc.me
Cc: Mathieu Malaterre <malat@debian.org>