Reqeust export symbol for API in arch/arm64/*

["최동혁/DONGHYEOK CHOE" <d7271.choe@samsung.com>]

Hello,

I am software engineer in charge of BSP (Samsung SOC vendor).

Recently, Google introduced GKI from Android R version.
We cannot use mainline API without 'export symbol' by the GKI policy.
But we want to make an arm64 specific vendor driver in {kernel source
root}/drivers/soc/samsung/*.

Could you support us to use the below APIs?

1. [register_kernel_break_hook]
To make runtime debug feature. We need architecture support.(break hook)
It's an architecture specific function. After cpu execute specific
instruction, A function with a parameter which is the context at that
time(the executing specific instruction) is performed. I am trying to
restore the locked context by using this fuction with  the el3 trap for
debugging hardlockup core(s).

2. [dump_backtrace]
Although 'dump_stack' is already supported, we need 'dump_backtrace' also.
Because we need lighten api to debug system. In some situation like bus
hang(HW bug), dump_stack highly likely make a problem again while printing
debug information.