aspeed: Load eMMC first boot area as a boot rom

aspeed: Load eMMC first boot area as a boot rom

The first boot area partition (64K) of the eMMC device should contain
an initial boot loader (u-boot SPL). Load it as a ROM only if an eMMC
device is available to boot from but no flash device is.

Signed-off-by: Cédric Le Goater <clg@kaod.org>
Reviewed-by: Andrew Jeffery <andrew@codeconstruct.com.au>
Tested-by: Andrew Jeffery <andrew@codeconstruct.com.au>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Tested-by: Philippe Mathieu-Daudé <philmd@linaro.org>