ec/system76/ec: Remove RPM calculation

System76 EC since system76/ec@80cfa91b9f ("acpi: Report RPM values
instead of raw tachometer values") performs the RPM calculation itself
and stores it  in EC RAM where previously the raw tachometer values were
saved. The SBIOS is no longer required to make the conversion.

Change-Id: I82a4e25a8ce0f274b2d98e7ff2b12595acf6c3c5
Signed-off-by: Tim Crawford <tcrawford@system76.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/83308
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Jeremy Soller <jeremy@system76.com>

src/ec/system76/ec/acpi/s76.asl

@@ -146,10 +146,6 @@ Device (S76D) {
 				Local1 = ^^PCI0.LPCB.EC0.RPM2
 			}
 		}
-		If (Local1 != 0) {
-			// 60 * (EC frequency / 120) / 2
-			Local1 = 2156250 / Local1
-		}
 		Return ((Local1 << 8) | Local0)
 	}