[PATCH] ram: rockchip: px30: add a config-based ddr selection

[Philipp Tomsich]

> On 01.10.2020, at 20:40, Heiko Stuebner <heiko at sntech.de> wrote:
> 
> From: Heiko Stuebner <heiko.stuebner at theobroma-systems.com>
> 
> The SRAM on the PX30 is not big enough to hold multiple DDR configs
> so it needs to be selected during build.
> 
> So far simply the DDR3 config was always selected and getting DDR4
> or LPDDR2/3 initialized would require a code modification.
> 
> So add Kconfig options similar to RK3399 to allow selecting the DDR4
> and LPDDR2/3 options instead, while DDR3 stays the default as before.
> 
> Signed-off-by: Heiko Stuebner <heiko.stuebner at theobroma-systems.com>

Reviewed-by: Philipp Tomsich <philipp.tomsich at theobroma-systems.com>