fs-resize: Add configurable game partition for Windows users

[AveyondFly]

Previously, all remaining space on the system disk was allocated to the storage partition. This approach may not be ideal for Windows users who wish to add games, as it doesn't provide a dedicated Windows known partition. Although Windows users can utilize Samba and USB methods for transferring game data, these methods tend to be slower compared to direct copying via a card reader, especially for large game files.

This commit introduces the ability to create a configurable "GAMES" partition. Users can now specify the desired size of the storage partition by creating a file named resize_storage_xG in the /flash partition before the first system startup (after flashing the image to the disk). The fs-resize script will then:

1. Resize the storage partition to end at xG.
2. Create a new "GAMES" partition using the remaining space on the disk.

If the resize_storage_xG file is not present, the fs-resize script will default to allocating all available space to the storage partition as before.

Example:

• To reserve storage partition ends with 50G and use the remaining space for the GAMES partition, create a file named resize_storage_50G in the /flash partition.