MAINTAINERS: add entry for intel_pstate

Add entry for intel_pstate.

Signed-off-by: Kristen Carlson Accardi <[e-mail]>
Signed-off-by: Rafael J. Wysocki <[e-mail]>

MAINTAINERS

···
 S:	Supported
 F:	drivers/idle/intel_idle.c
 
+INTEL PSTATE DRIVER
+M:	Kristen Carlson Accardi <[e-mail]>
+L:	[e-mail]
+S:	Supported
+F:	drivers/cpufreq/intel_pstate.c
+
 INTEL FRAMEBUFFER DRIVER (excluding 810 and 815)
 M:	Maik Broemme <[e-mail]>
 L:	[e-mail]