phy: cadence: Sierra: Move all reset_control_get*() to a separate function

No functional change. Group devm_reset_control_get() and
devm_reset_control_get_optional() to a separate function.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Reviewed-by: Philipp Zabel <p.zabel@pengutronix.de>
Link: https://lore.kernel.org/r/20210319124128.13308-7-kishon@ti.com


Signed-off-by: Vinod Koul <vkoul@kernel.org>