ARM: Add CONFIG_ARMV7_SECURE_MAX_SIZE and check size of secure section

As the PSCI implementation grows, we might exceed the size of the secure
memory that holds the firmware.

Add a configurable CONFIG_ARMV7_SECURE_MAX_SIZE so platforms can define
how much secure memory is available. The linker then checks the size of
the whole secure section against this.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>