[RFC] rockchip: rk3308: fix "same-as-spl" bug in boot devices order

[Pegorer Massimo]

Value "same-as-spl" in uboot,spl-boot-order attribute is not working for
boards based on rk3308 due to mismatch between definitions in rk3308.c
and those in rk3308.dtsi: in the first file boot devices are defined as
"/mcc at ff4....", while in the DTSI they are "dwmmc at ff4...".

Of course it could be fixed updating rk3308.c to match DTSI definitions.
Anyway, I've noticed that almost all rockchip DTS/DTSI files, in the past,
have been moved from using "dwmmc" to "mmc". And rk3308.dtsi in Linux
kernel sources too, it has been already updated to "mmc".

Therefore, other two alternative ways to fix the problem are: replace
"dwmmc" with "mmc" in rk3308.dtsi; align rk3308.dtsi with Linux kernel
one. Which do you suggest? I would prefer the last, but there are several
other differences between u-boot and linux DTSI files.

A second point is: I need to add bootph-all to sdmmc because some models
of Rock Pi S are missing of SDNAND/eMMC and the only bootable device is the
uSD. Is it preferrable to add it in the common rk3308-u-boot.dsi or in the
board specific rk3308-rock-pi-s-u-boot.dtsi?

Thanks. Regards,
Massimo