arm64: renesas: Add Renesas R-Car V4H SPL implementation

arm64: renesas: Add Renesas R-Car V4H SPL implementation

Add support for building U-Boot SPL for Renesas R-Car Gen4 R8A779G0 V4H SoC.
The SPL initializes the DBSC5 DRAM controller, RT-VRAM and loads and starts
U-Boot proper on the Cortex-A76 core.

The SoC BootROM can not boot the CA76 core directly, instead the SPL starts
on the CR52 core which immediately brings up the CA76 core, which in turn
starts executing the actual SPL. This is achieved by placing a tiny bit of
precompiled Aarch32 code at the very beginning of the SPL. The code consists
of some 32 instructions, uses APMU to configure CA76 start address to offset
0x80 Bytes from start of the SPL, and uses APMU to start the CA76 core. The
code parts the CR52 core in an endless loop once the CA76 core got started.

The 32 instructions are completely arbitrary number, so is the offset 0x80
Bytes from start of SPL, because 0x80 = 128 decimal and 128 / 4 bytes per
instruction is 32 instructions. The 32 instructions turned out to be enough
to started the CA76 and 0x80 is nicely aligned.

Once the SPL completes hardware initialization, the SPL loads U-Boot proper.
The u-boot.itb proper fitImage contains 64bit build on u-boot-nodtb.bin and
a DT for R8A779G0 V4H White Hawk board and is generated by binman. The
u-boot.itb is loaded from SPI NOR offset 0x80000.

In order to install this setup on an existing R8A779G0 V4H White Hawk board,
build using r8a779g0_whitehawk_defconfig, generate SPI NOR image flash.bin
and write flash.bin to SPI NOR offset 0x0 . Finally, configure board MD pin
switches according to the R8A779G0 V4H White Hawk board documentation for
40 MHz SPI NOR boot using DMA and restart the board.

Signed-off-by: Marek Vasut <[email protected]>