[yocto] [meta-rockchip][PATCH v2 4/5] classes: rockchip-gpt-img: add

[Trevor Woerner]

> what about use BOOT_IMG = "boot-${MACHINE}-${DATETIME}.img" instead? That
> will leave the previous build for debug and avoid trouble.

Using boot-${MACHINE}-${DATETIME}.img doesn't work, it leads to the following
errors:

	ERROR: When reparsing /z/rockchip/master/layers/openembedded-core/meta/recipes-core/images/core-image-minimal.bb.do_image_rockchip_gpt_img, the basehash value changed from 7150ddd4bffcc76eed6ec85216596f3b to 2c30fda706826e991aaf953180edc3b2. The metadata is not deterministic and this needs to be fixed.