platform/x86/amd: amd_3d_vcache: Add sysfs ABI documentation

Add documentation for the amd_3d_vcache sysfs bus platform driver
interface so that userspace applications can use it to change mode
preferences, either frequency or cache.

Co-developed-by: Perry Yuan <[e-mail]>
Signed-off-by: Perry Yuan <[e-mail]>
Co-developed-by: Mario Limonciello <[e-mail]>
Signed-off-by: Mario Limonciello <[e-mail]>
Reviewed-by: Shyam Sundar S K <[e-mail]>
Reviewed-by: Armin Wolf <[e-mail]>
Reviewed-by: Ilpo Järvinen <[e-mail]>
Signed-off-by: Basavaraj Natikar <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Ilpo Järvinen <[e-mail]>

Documentation/ABI/testing/sysfs-bus-platform-drivers-amd_x3d_vcache

···
+What:		/sys/bus/platform/drivers/amd_x3d_vcache/AMDI0101:00/amd_x3d_mode
+Date:		November 2024
+KernelVersion:	6.13
+Contact:	Basavaraj Natikar <[e-mail]>
+Description:	(RW) AMD 3D V-Cache optimizer allows users to switch CPU core
+		rankings dynamically.
+
+		This file switches between these two modes:
+		- "frequency" cores within the faster CCD are prioritized before
+		those in the slower CCD.
+		- "cache" cores within the larger L3 CCD are prioritized before
+		those in the smaller L3 CCD.

MAINTAINERS

···
 R:	Mario Limonciello <[e-mail]>
 L:	[e-mail]
 S:	Supported
+F:	Documentation/ABI/testing/sysfs-bus-platform-drivers-amd_x3d_vcache
 F:	drivers/platform/x86/amd/x3d_vcache.c
 
 AMD ADDRESS TRANSLATION LIBRARY (ATL)