ARM: dts: aspeed: Add 128M alt flash layout to NVIDIA MSX4

ARM: dts: aspeed: Add 128M alt flash layout to NVIDIA MSX4

Add a 128M layout for the BMC flash chip we didn't boot from. Including
this allows the user to write to each partition on the alternate spi
chip. This dtsi follows the existing standard of using the same layout
as non alt version and prepending `alt` to each partition's name.

[arj: Update subject, elide test demonstration]

Signed-off-by: Marc Olberding <molberding@nvidia.com>
Link: https://patch.msgid.link/20260120-alt-128-v4-1-0e5c491a532c@nvidia.com
Signed-off-by: Andrew Jeffery <andrew@codeconstruct.com.au>