arm64: dts: NS2: reserve memory for Nitro firmware

[ Upstream commit 0cc878d678444392ca2a31350f89f489593ef5bb ]

Nitro firmware is loaded into memory by the bootloader at a specific
location.  Set this memory range aside to prevent the kernel from using
it.

Signed-off-by: Jon Mason <jon.mason@broadcom.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>