configs: am65x_evm_r5: enable driver for fixed regulators

Some of the regulators we need to successfully boot are fixed
regulators. Enable the driver to properly probe them.

Tested-by: Tom Rini <trini@konsulko.com>
Signed-off-by: Bryan Brattlof <bb@ti.com>
Reviewed-by: Nishanth Menon <nm@ti.com>