ARM: OMAP2+: Remove bogus warnings for machines without twl PMIC

In general we want to see a quiet dmesg output with no errors or warnings
unless something is really wrong and needs attention. We currently see
these bogus warnings on boot:

twl: not initialized
twl6030_uv_to_vsel:OUT OF RANGE! non mapped vsel for 1375000 Vs max 1316660
twl6030_uv_to_vsel:OUT OF RANGE! non mapped vsel for 1375000 Vs max 1316660
twl6030_uv_to_vsel:OUT OF RANGE! non mapped vsel for 1375000 Vs max 1316660
twl6030_uv_to_vsel:OUT OF RANGE! non mapped vsel for 1375000 Vs max 1316660
...

Let's avoid these by checking if a device tree node for cpcap PMIC exists.

Cc: Merlijn Wajer <merlijn@wizzup.org>
Cc: Pavel Machek <pavel@ucw.cz>
Cc: Sebastian Reichel <sre@kernel.org>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Tony Lindgren <tony@atomide.com>