drives: cmake: zephyr_library_property(ALLOW_EMPTY TRUE) on drivers lib

This commit now sets the Zephyr library property `ALLOW_EMPTY` to
silence the warning:
`No SOURCES given to Zephyr library: drivers__interrupt_controller`

Signed-off-by: Torsten Rasmussen <Torsten.Rasmussen@nordicsemi.no>
1 file changed