MAINTAINERS: update powerplay and swsmu

Evan is no longer maintaining powerplay and swsmu.
Add Kenneth Feng as his replacement.
Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: Kenneth Feng <kenneth.feng@amd.com>

MAINTAINERS

@@ -1092,7 +1092,7 @@ F:	Documentation/ABI/testing/sysfs-amd-pmf
 F:	drivers/platform/x86/amd/pmf/
 
 AMD POWERPLAY AND SWSMU
-M:	Evan Quan <evan.quan@amd.com>
+M:	Kenneth Feng <kenneth.feng@amd.com>
 L:	amd-gfx@lists.freedesktop.org
 S:	Supported
 T:	git https://gitlab.freedesktop.org/agd5f/linux.git