ARM: 5624/1: Document cache aliasing region

Augment the memory.txt file for ARM to list the cache aliasing
region ffff4000-fffffff.
Signed-off-by: NLinus Walleij <linus.walleij@stericsson.com>
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>

Documentation/arm/memory.txt

@@ -21,6 +21,8 @@ ffff8000	ffffffff	copy_user_page / clear_user_page use.
 				For SA11xx and Xscale, this is used to
 				setup a minicache mapping.
 
+ffff4000	ffffffff	cache aliasing on ARMv6 and later CPUs.
+
 ffff1000	ffff7fff	Reserved.
 				Platforms must not use this address range.