powerpc/fsl_uli1575: Mark uli_exclude_device() as static

Function uli_exclude_device() is not used outside of the fsl_uli1575.c
source file anymore. So mark it as static and remove public prototype.

Signed-off-by: Pali Rohár <pali@kernel.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230409000812.18904-9-pali@kernel.org