feat(plat/rcar3): add process to back up X6 and X7 register's value

Because the x6 and x7 registers will be overwritten by the callee function,
added the processing the register's value push to/pop from stack memory.

Signed-off-by: Hideyuki Nitta <hideyuki.nitta.jf@hitachi.com>
Signed-off-by: Toshiyuki Ogasahara <toshiyuki.ogasahara.bo@hitachi.com>
Signed-off-by: Yoshifumi Hosoya <yoshifumi.hosoya.wj@renesas.com>
Change-Id: I5351a008d3b208a30a8bc8651b8d9b4d1a02a8e8
1 file changed