phy: phy-snps-eusb2: make reset control optional

Not all SoCs expose the reset line controls to the kernel, so make them
optional.

Signed-off-by: Ivaylo Ivanov <ivo.ivanov.ivanov1@gmail.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Link: https://lore.kernel.org/r/20250504144527.1723980-8-ivo.ivanov.ivanov1@gmail.com


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