board: toradex: aquila-am69: Fix memory size setup logic

board: toradex: aquila-am69: Fix memory size setup logic

The hardware configuration pins are used both to select the DDR
configuration and to determine the installed memory size.

On Aquila AM69, the DDR timing patch is applied in the R5 SPL, while the
memory size fixup for the next-stage U-Boot DT is done later in the A72
SPL path.
The previous immplementation was not taking in account that the hw_cfg
value is lost both during SPL execution (board_init_f and board_init_r)
and between SPL and U-Boot proper.

Fix this by reading the hardware configuration pins when the memory size
is actually needed:
- in the R5 SPL, to select the correct DDR configuration
- in the A72 SPL, to fix up the U-Boot DT memory size and bank layout

Fixes: 3f0528882c0d ("board: toradex: add aquila am69 support")
Signed-off-by: Emanuele Ghidoli <emanuele.ghidoli@toradex.com>
Acked-by: Francesco Dolcini <francesco.dolcini@toradex.com>