misc: sram: Integrate protect-exec reserved sram area type

Introduce a new "protect-exec" reserved sram area type which is
makes use of the the existing functionality provided for the "pool"
sram region type for use with the genalloc framework and with the
added requirement that it be maintained as read-only and executable
while allowing for an arbitrary number of drivers to share the space.

This introduces a common way to maintain a region of sram as read-only
and executable and also introduces a helper function, sram_exec_copy,
which allows for copying data to this protected region while maintaining
locking to avoid conflicts between multiple users of the same space. A
region of memory that is marked with the "protect-exec" flag in the
device tree also has the requirement of providing a page aligned block
of memory so that the page attribute manipulation does not affect
surrounding regions.

Also, selectively enable this only for builds that support set_memory_*
calls, for now just ARM, through the use of Kconfig.

Signed-off-by: Dave Gerlach <d-gerlach@ti.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/devicetree/bindings/sram/sram.txt

@@ -42,6 +42,12 @@ Optional properties in the area nodes:
          and in use by another device or devices
 - export : indicates that the reserved SRAM area may be accessed outside
            of the kernel, e.g. by bootloader or userspace
+- protect-exec : Same as 'pool' above but with the additional
+		 constraint that code wil be run from the region and
+		 that the memory is maintained as read-only, executable
+		 during code execution. NOTE: This region must be page
+		 aligned on start and end in order to properly allow
+		 manipulation of the page attributes.
 - label : the name for the reserved partition, if omitted, the label
           is taken from the node name excluding the unit address.