[Reboot] remove exec from the platform_reboot call when executing reboot in kdump kernel

[DennisChiuEC]

What I did

Remove exec from the platform_reboot call to handle any hang issue during reboot in kdump kernel

How I did it

How to verify it

Trigger kernel panic after uninstalling the platform driver and check if the device can reboot without hang.

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)