hw/mips/malta: Use bootloader generator API for nanoMIPS CPUs (1/5)

hw/mips/malta: Use bootloader generator API for nanoMIPS CPUs (1/5)

Similarly to how commit 0c8427baf0 ("hw/mips/malta: Use bootloader
helper to set BAR registers") converted write_bootloader(), convert
the equivalent write_bootloader_nanomips(), allowing us to modify
the bootloader code more easily in the future.

Part 1/5: Convert PCI0 MEM1 BAR setup

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20221211204533.85359-7-philmd@linaro.org>