arm: Switch to -mno-unaligned-access when supported by the compiler

When we tell the compiler to optimize for ARMv7 (and ARMv6 for that
matter) it assumes a default of SCTRL.A being cleared and unaligned
accesses being allowed and fast at the hardware level.  We set this bit
and must pass along -mno-unaligned-access so that the compiler will
still breakdown accesses and not trigger a data abort.

To better help understand the requirements of the project with respect
to unaligned memory access, the
Documentation/unaligned-memory-access.txt file has been added as
doc/README.unaligned-memory-access.txt and is taken from the v3.14-rc1
tag of the kernel.

Cc: Albert ARIBAUD <albert.u.boot@aribaud.net>
Cc: Mans Rullgard <mans@mansr.com>
Signed-off-by: Tom Rini <trini@ti.com>
diff --git a/README b/README
index 5b7dec9..3fdd119 100644
--- a/README
+++ b/README
@@ -1726,7 +1726,7 @@
 
 		If this option is set, then U-Boot will prevent the environment
 		variable "splashimage" from being set to a problematic address
-		(see README.displaying-bmps and README.arm-unaligned-accesses).
+		(see README.displaying-bmps).
 		This option is useful for targets where, due to alignment
 		restrictions, an improperly aligned BMP image will cause a data
 		abort. If you think you will not have problems with unaligned