hw/arm: Load -bios image as a boot ROM for npcm7xx

hw/arm: Load -bios image as a boot ROM for npcm7xx

If a -bios option is specified on the command line, load the image into
the internal ROM memory region, which contains the first instructions
run by the CPU after reset.

If -bios is not specified, the vbootrom included with qemu is loaded by
default.

Reviewed-by: Tyrone Ting <kfting@nuvoton.com>
Reviewed-by: Cédric Le Goater <clg@kaod.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Tested-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Havard Skinnemoen <hskinnemoen@google.com>
Message-id: 20200911052101.2602693-8-hskinnemoen@google.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>