ARM: arch-meson: build memory banks using reported memory from registers

ARM: arch-meson: build memory banks using reported memory from registers

As discussed at [1], the Amlogic Meson GX SoCs can embed a BL31 firmware
and a secondary BL32 firmware.
Since mid-2017, the reserved memory address of the BL31 firmware was moved
and grown for security reasons.

But mainline U-Boot and Linux has the old address and size fixed.

These SoCs have a register interface to get the two firmware reserved
memory start and sizes.

This patch adds a dynamic reservation of the memory zones in the device tree bootmem
reserved memory zone used by the kernel in early boot.
To be complete, the memory zones are also added to the EFI reserved zones.

Depends on patchset "Add support for Amlogic GXL Based SBCs" at [2].

[1] http://lists.infradead.org/pipermail/linux-amlogic/2017-October/004860.html
[2] http://lists.infradead.org/pipermail/linux-amlogic/2017-November/005410.html

Changes since v1:
- switched the #if to if(IS_ENABLED()) to compile all code paths
- renamed function to meson_board_add_reserved_memory()
- added a mem.h header with comment
- updated all boards ft_board_setup()

Changes since RFC v2:
- reduced preprocessor load
- kept Odroid-C2 static memory mapping as exception

Changes since RFC v1:
- switch to fdt rsv mem table and efi reserve memory
- replaced in_le32 by readl()

Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
[trini: Fix warning on khadas-vim over missing <asm/arch/mem.h>
Signed-off-by: Tom Rini <trini@konsulko.com>