ARM: 8854/1: drop -mauto-it

The assembler option -mauto-it is no longer a valid option. The last
remaining references have been removed from the documentation in
July 2009 [0].

The currently supported binutils version is 2.20 (released in
September 2009) or higher where gas supports -mimplicit-it=always.
Drop the fallback to -mauto-it and use -mimplicit-it=always only.

[0] https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=529707530657a333a304c651c808ea630c955223

Signed-off-by: Stefan Agner <stefan@agner.ch>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>