ARM: uaccess: provide uaccess_save_and_enable() and uaccess_restore()

Provide uaccess_save_and_enable() and uaccess_restore() to permit
control of userspace visibility to the kernel, and hook these into
the appropriate places in the kernel where we need to access
userspace.

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

diff --cc arch/arm/include/asm/futex.h
Simple merge

diff --cc arch/arm/include/asm/uaccess.h
Simple merge

diff --cc arch/arm/kernel/armksyms.c
Simple merge

diff --cc arch/arm/lib/clear_user.S
Simple merge

diff --cc arch/arm/lib/copy_from_user.S
Simple merge

diff --cc arch/arm/lib/copy_to_user.S
Simple merge

diff --cc arch/arm/lib/uaccess_with_memcpy.c
Simple merge