[DellEMC] S6100 I2C Enumeration Segregation

[santhosh-kt]

- What I did
[DellEMC] S6100 I2C Enumeration Segregation

- How I did it

• Segregation of I2C related initializations in a separate script s6100_i2c_enumeration.sh.
• Running a new service s6100-i2c-enumerate.service asynchronously during fast-reboot and warm-reboot to reduce the load in rc.local that runs the new script.

- How to verify it

• Attached test cases:
  Test cases.txt

- Description for the changelog

On branch s6100-i2c-enumerate
Changes to be committed:
(use "git reset HEAD ..." to unstage)

    modified:   platform/broadcom/sonic-platform-modules-dell/debian/platform-modules-s6100.install
    copied:     platform/broadcom/sonic-platform-modules-dell/s6100/scripts/s6100_platform.sh -> platform/broadcom/sonic-platform-modules-dell/s6100/scripts/s6100_i2c_enumeration.sh
    modified:   platform/broadcom/sonic-platform-modules-dell/s6100/scripts/s6100_platform.sh
    new file:   platform/broadcom/sonic-platform-modules-dell/s6100/systemd/s6100-i2c-enumerate.service

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