Currently, the Raspberry Pi PiSP Backend (BE) ISP is only present on the
Broadcom BCM2712-based Raspberry Pi 5. Hence add a dependency on
ARCH_BCM2835, to prevent asking the user about this driver when
configuring a kernel without Broadcom BCM2835 family support. The
dependency can be relaxed if/when the encoder appears on other SoC
families.
Fixes: 12187bd5d4f8c128 ("media: raspberrypi: Add support for PiSP BE")
Signed-off-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>