UPSTREAM: arch/arm: Add armv7-r configuration

This change adds armv7-r support for all stages.

armv7-r is an ARM processor based on the Cortex-R series.

Currently, there is support for armv7-a and armv7-m and
armv7-a files has been modfied to accommodate armv7-r by
adding ENV_ARMV7_A, ENV_ARMV7_R and ENV_ARMV7_M constants
to src/include/rules.h.

armv7-r exceptions support will added in a later time.

BUG=None
BRANCH=None
TEST=None

Signed-off-by: Hakim Giydan <hgiydan@marvell.com>
Reviewed-on: https://review.coreboot.org/15335
Tested-by: build bot (Jenkins)
Reviewed-by: Martin Roth <martinroth@google.com>

Change-Id: If94415d07fd6bd96c43d087374f609a2211f1885
Reviewed-on: https://chromium-review.googlesource.com/384968
Commit-Ready: Furquan Shaikh <furquan@chromium.org>
Tested-by: Furquan Shaikh <furquan@chromium.org>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

util/xcompile/xcompile

@@ -316,7 +316,7 @@ arch_config_arm() {
 	TBFDARCHS="littlearm"
 	TCLIST="armv7-a armv7a arm"
 	TWIDTH="32"
-	TSUPP="arm armv4 armv7 armv7_m"
+	TSUPP="arm armv4 armv7 armv7_m armv7_r"
 	TABI="eabi"
 }