ARM: 7068/1: process: change from __backtrace to dump_stack in show_regs

Currently, show_regs calls __backtrace which does
nothing if CONFIG_FRAME_POINTER is not set. Switch to
dump_stack which handles both CONFIG_FRAME_POINTER and
CONFIG_ARM_UNWIND correctly.

__backtrace is now superseded by dump_stack in general
and show_regs was the last caller so remove __backtrace
as well.

Change-Id: I396677df8bc22bf28e4486f2bfb155c516a3d452
Signed-off-by: Laura Abbott <lauraa@codeaurora.org>
Acked-by: Nicolas Pitre <nicolas.pitre@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>