[ARM] 3761/1: fix armv4t breakage after adding thumb interworking to userspace helpers

Patch from Lennert Buytenhek

On armv4t systems, we have always compiled the kernel with -march=armv4
instead of -march=armv4t, which means that any use of bx will bomb out.

Commit ba9b5d76

 introduced the use of
bx in the kernel, which means we need to compile with -march=armv4t on
armv4t systems now.

Signed-off-by: Lennert Buytenhek <buytenh@wantstofly.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>