rpi3: Move rpi3_hw.h header file to include/rpi_hw.h

With the advent of Raspberry Pi 4 support, we need to separate some
board specific headers between the RPi3 and RPi4.
Rename and move the "rpi3_hw.h" header, so that .c files just include
rpi_hw.h, and automatically get the correct version.

Change-Id: I03b39063028d2bee1429bffccde71dddfe2dcde8
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
diff --git a/plat/rpi/rpi3/rpi3_pm.c b/plat/rpi/rpi3/rpi3_pm.c
index 4f586b5..b79e273 100644
--- a/plat/rpi/rpi3/rpi3_pm.c
+++ b/plat/rpi/rpi3/rpi3_pm.c
@@ -15,7 +15,7 @@
 #include <lib/psci/psci.h>
 #include <plat/common/platform.h>
 
-#include "rpi3_hw.h"
+#include <rpi_hw.h>
 
 /* Make composite power state parameter till power level 0 */
 #if PSCI_EXTENDED_STATE_ID