Add RPi target rpi_arm64

This target is needed for U-Boot capable to work with
Raspberry Pi 3 and 4.

Signed-off-by: Denis Pynkin <denis.pynkin@collabora.com>

debian/targets

@@ -213,6 +213,9 @@ arm64  rockchip        rock-pi-4-rk3399 /usr/lib/arm-trusted-firmware/rk3399/bl3
 # Ryan Finnie <ryan@finnie.org>
 arm64	rpi		rpi_3		u-boot.bin
 
+# Denis Pynkin <denis.pynkin@collabora.com>
+arm64	rpi		rpi_arm64	u-boot.bin
+
 # Rodrigo Exterckötter Tjäder <rodrigo@tjader.xyz>
 arm64	sunxi		a64-olinuxino	/usr/lib/arm-trusted-firmware/sun50i_a64/bl31.bin u-boot.bin spl/sunxi-spl.bin u-boot-nodtb.bin arch/arm/dts/sun50i-a64-olinuxino.dtb u-boot.itb