[warm-reboot] Add support to pass extra kernel cmdline parameters

[pavannaregundi]

What I did

Add support to optionally pass extra kernel command line arguments during warm-reboot kexec load.

How I did it

Extra command line arguments can be supplied from variable 'KEXEC_LOAD_EXTRA_CMDLINE_LINUX' in "installer.conf" present in device hwsku folder.

# cat installer.conf 
KEXEC_LOAD_EXTRA_CMDLINE_LINUX="<extra command line arguments>"

How to verify it

Triggered warm-reboot on Marvell AC5XRD platform and checked for successful warmboot.

Previous command output (if the output of a command-line utility has changed)

New command output (if the output of a command-line utility has changed)

[pavannaregundi]

@vaibhavhd @saiarcot895 can you please review