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_common.c b/plat/rpi/rpi3/rpi3_common.c
index 9b10974..85a26c2 100644
--- a/plat/rpi/rpi3/rpi3_common.c
+++ b/plat/rpi/rpi3/rpi3_common.c
@@ -16,7 +16,7 @@
 #include <drivers/ti/uart/uart_16550.h>
 #include <lib/xlat_tables/xlat_tables_v2.h>
 
-#include "rpi3_hw.h"
+#include <rpi_hw.h>
 #include "rpi3_private.h"
 
 #define MAP_DEVICE0	MAP_REGION_FLAT(DEVICE0_BASE,			\