tegra124: Reserve secure RAM using MC_SECURITY_CFG{0, 1}_0

These registers can be used to prevent non-secure world from accessing a
megabyte aligned region of RAM, use them to protect the u-boot secure monitor
code.

At first I tried to do this from s_init(), however this inexplicably causes
u-boot's networking (e.g. DHCP) to fail, while networking under Linux was fine.

So instead I have added a new weak arch function protect_secure_section()
called from relocate_secure_section() and reserved the region there. This is
better overall since it defers the reservation until after the sec vs. non-sec
decision (which can be influenced by an envvar) has been made when booting the
os.

Signed-off-by: Ian Campbell <ijc@hellion.org.uk>
[Jan: tiny style adjustment]
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Thierry Reding <treding@nvidia.com>
Tested-by: Thierry Reding <treding@nvidia.com>
Tested-by: Ian Campbell <ijc@hellion.org.uk>
Signed-off-by: Tom Warren <twarren@nvidia.com>

arch/arm/include/asm/system.h

@@ -77,6 +77,7 @@ void armv8_switch_to_el1(void);
 void gic_init(void);
 void gic_send_sgi(unsigned long sgino);
 void wait_for_wakeup(void);
+void protect_secure_region(void);
 void smp_kick_all_cpus(void);
 
 void flush_l3_cache(void);