[U-Boot] [RFC]Remove SPL Framework with a MACRO

[Kever Yang]

Hi guys,

    Some of our SoCs have very critical sram size, which just enough for
DRAM init code only,

so that we have to remove all the other drivers and framwork to make it
work.

    We are now using a MACRO named TPL_TINY_FRAMEWORK, to remove all the
SPL framework

in TPL, see https://github.com/rockchip-linux/u-boot/tree/release/.

    We want a separate code like TPL but don't want all those SPL
framework, and we can re-use

the driver code like sdram, timer, debug uart, clock...

    Is there any similar implementation in other platform can be
referenced or any suggestion?


    I want to make it upstream, and then Rockchip platform code
structure will like this:

TINY_TPL(for ddr init only, sram)
    |
    v
Back to bootRom
    |
    v
SPL(for load trust and u-boot, ddr)
    |
    v
U-Boot Proper(via trust)
    Only few SoCs will not use this flow, like RK3399 using SPL+U-Boot
without  TPL for it have enough sram size.

    Then we don't have handle the SPL size limit from time to time, and
all platform can support trust OS.


Thanks,

- Kever