raspberrypi4-64: Remove the 3G RAM limitation

The PCIe bounce buffers were ported[1] in the kernel so we can remove
this limitation now.

[1] raspberrypi/linux#3144

Signed-off-by: Andrei Gherzan <andrei@gherzan.ro>

conf/machine/raspberrypi4-64.conf

@@ -31,6 +31,6 @@ KERNEL_IMAGETYPE_UBOOT ?= "Image"
 KERNEL_IMAGETYPE_DIRECT ?= "Image"
 KERNEL_BOOTCMD ?= "booti"
 
-RPI_EXTRA_CONFIG ?= "\n# Force arm in 64bit mode. See: https://github.com/raspberrypi/firmware/issues/1193.\narm_64bit=1\n\n# Limit RAM to 3G. See: https://github.com/raspberrypi/linux/issues/3093\ntotal_mem=3072"
+RPI_EXTRA_CONFIG ?= "\n# Force arm in 64bit mode. See: https://github.com/raspberrypi/firmware/issues/1193.\narm_64bit=1"
 
 ARMSTUB ?= "armstub8-gic.bin"