Change in coreboot[master]: ec/google: Add support for ARTG method

[Paul Menzel (Code Review)]

Attention is currently required from: Varshit B Pandya, Tim Wawrzynczak, Rizwan Qureshi, Sumeet R Pawnikar, Eric Lai.
Paul Menzel has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/63949 )

Change subject: ec/google: Add support for ARTG method
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Patch Set 2:

(1 comment)

Commit Message:

https://review.coreboot.org/c/coreboot/+/63949/comment/edb6be11_f4cb41d0 
PS2, Line 9: As per Intel Dynamic Tunning revision 1.3.13 add support for
           : ARTG under _SB.DPTF.TPWR device
           : 
           : Chromeec is passing ARTG value in multiples of 50mW to save
           : space, driver expects this in mW hence multiplying it by 50
           : in ACPI mehod.
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