unicore32: move rtc-puv3.c to drivers/rtc directory

The patch moves rtc driver for PKUnity-v3 SoC from arch/unicore32/kernel/
to drivers/rtc/, with renaming it to rtc-puv3.c.
Also, Kconfig, Makefile, and MAINTAINERS are modified correspondingly.

Signed-off-by: Guan Xuetao <gxt@mprc.pku.edu.cn>
Acked-by: Arnd Bergmann <arnd@arndb.de>
diff --git a/MAINTAINERS b/MAINTAINERS
index b5ea4d0..bbe49d8 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -4945,6 +4945,7 @@
 F:	drivers/input/serio/i8042-unicore32io.h
 F:	drivers/i2c/busses/i2c-puv3.c
 F:	drivers/video/fb-puv3.c
+F:	drivers/rtc/rtc-puv3.c
 
 PMC SIERRA MaxRAID DRIVER
 M:	Anil Ravindranath <anil_ravindranath@pmc-sierra.com>