power: pmic: Provide DM_PMIC support for tps65217 driver

The tps65217 PMIC driver is used with am335x SoC based designs.

It is used in the SPL (MLO) as well, so the DM conversion only is
for u-boot proper.

This driver only allows simple reading/writing/dumping of the content
of its registers and requires the DM_I2C for proper operation.

Signed-off-by: Lukasz Majewski <lukma@denx.de>
Reviewed-by: Jaehoon Chung <jh80.chung@samsung.com>