soc/tegra: Make regulator couplers depend on CONFIG_REGULATOR

The regulator coupler drivers now use regulator-driver API function that
isn't available during compile-testing. Make regulator coupler drivers
dependent on CONFIG_REGULATOR in Kconfig.

Fixes: 03978d42 ("soc/tegra: regulators: Bump voltages on system reboot")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Acked-by: Jon Hunter <jonathanh@nvidia.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>