[FS#1408] Separate device-specific config files in base files & remove white-spaces in bash files

[LEDE Bugs]

A new Flyspray task has been opened.  Details are below. 

User who did this - Shang Jia (zhoushiyi213) 

Attached to Project - OpenWrt/LEDE Project
Summary - Separate device-specific config files in base files & remove white-spaces in bash files
Task Type - Feature Request
Category - Base system
Status - Unconfirmed
Assigned To - 
Operating System - All
Severity - Medium
Priority - Very Low
Reported Version - All
Due in Version - Undecided
Due Date - Undecided
Details - The redundant config files for other targets in the same arch (e.g. in /etc/diag.sh, /lib/preinit/, /etc/board.d) can take quite a bit of space (a few of kB after sfs, especially for popular archs like ar71xx). Separating config files into board-specific base-files.ipk packages can be very useful for devices with limited flash space.

Also, it will be much helpful to include an option/script in the image builder for auto-removing comments and white-space in all bash and lua files since this will also be much useful for devices with 4MB flash.

More information can be found at the following URL:
https://bugs.openwrt.org/index.php?do=details&task_id=1408