src: Remove redundant use of ACPI offset(0)

IASL version 20180927 and greater, detects Unnecessary/redundant uses of
the Offset() operator within a Field Unit list.
It then sends a remark "^ Unnecessary/redundant use of Offset"

example:
    OperationRegion (OPR1, SystemMemory, 0x100, 0x100)
    Field (OPR1)
    {
        Offset (0),     // Never needed
        FLD1, 32,
        Offset (4),     // Redundant, offset is already 4 (bytes)
        FLD2, 8,
        Offset (64),    // OK use of Offset.
        FLD3, 16,
    }

We will have those remarks:
dsdt.asl     14:         Offset (0),
Remark   2158 -                 ^ Unnecessary/redundant use of Offset operator

dsdt.asl     16:         Offset (4),
Remark   2158 -                 ^ Unnecessary/redundant use of Offset operator

Change-Id: I260a79ef77025b4befbccc21f5999f89d90c1154
Signed-off-by: Elyes HAOUAS <ehaouas@noos.fr>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/43283
Reviewed-by: Felix Held <felix-coreboot@felixheld.de>
Reviewed-by: Marshall Dawson <marshalldawson3rd@gmail.com>
Reviewed-by: Jason Glenesk <jason.glenesk@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/soc/intel/skylake/acpi/globalnvs.asl

@@ -17,7 +17,6 @@ OperationRegion (GNVS, SystemMemory, NVSA, 0x2000)
 Field (GNVS, ByteAcc, NoLock, Preserve)
 {
 	/* Miscellaneous */
-	Offset (0x00),
 	OSYS,	16,	// 0x00 - Operating System
 	SMIF,	8,	// 0x02 - SMI function
 	PRM0,	8,	// 0x03 - SMI function parameter

src/soc/intel/skylake/acpi/xhci.asl

@@ -83,7 +83,6 @@ Device (XHCI)
 	OperationRegion (XPRT, PCI_Config, 0x00, 0x100)
 	Field (XPRT, AnyAcc, NoLock, Preserve)
 	{
-		Offset (0x0),
 		DVID, 16,	/* VENDORID */
 		Offset (0x10),
 		, 16,