drm/vc4: Fix build error when CONFIG_DRM_VC4=y && CONFIG_RASPBERRYPI_FIRMWARE=m

If CONFIG_DRM_VC4=y, CONFIG_RASPBERRYPI_FIRMWARE=m, CONFIG_COMPILE_TEST=n,
bulding fails:

drivers/gpu/drm/vc4/vc4_drv.o: In function `vc4_drm_bind':
vc4_drv.c:(.text+0x320): undefined reference to `rpi_firmware_get'
vc4_drv.c:(.text+0x320): relocation truncated to fit: R_AARCH64_CALL26 against undefined symbol `rpi_firmware_get'
vc4_drv.c:(.text+0x34c): undefined reference to `rpi_firmware_property'
vc4_drv.c:(.text+0x34c): relocation truncated to fit: R_AARCH64_CALL26 against undefined symbol `rpi_firmware_property'
vc4_drv.c:(.text+0x354): undefined reference to `rpi_firmware_put'
vc4_drv.c:(.text+0x354): relocation truncated to fit: R_AARCH64_CALL26 against undefined symbol `rpi_firmware_put'

Make DRM_VC4 depends on RASPBERRYPI_FIRMWARE || (COMPILE_TEST && !RASPBERRYPI_FIRMWARE) to fix this.

Fixes: c406ad5e ("drm/vc4: Notify the firmware when DRM is in charge")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Zheng Bin <zhengbin13@huawei.com>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://patchwork.freedesktop.org/patch/msgid/20220411024325.3968413-1-zhengbin13@huawei.com