drivers: display: Select LED_STRIP when LED_STRIP_MATRIX is enabled

The LED_STRIP driver is not enabled by default on all boards. As a result,
building the LED_STRIP_MATRIX display driver fails if LED_STRIP is not
manually enabled.

To address this, this commit changes the dependency from `depends on` to
`select`, ensuring that the required driver is automatically enabled and
build failures are avoided.

Signed-off-by: Chen Xingyu <hi@xingrz.me>