firmware: Initial compiler built-in stack protector support

Add __stack_chk_fail() and __stack_chk_guard variable which are used by
compiler built-in stack protector.

This patch just try to support stack-protector so the value of the stack
guard variable is simply fixed for now. It could be improved by
deriving from a random number generator, such as Zkr extension or any
platform-specific random number sources.

Introduce three configurations for the stack protector:
1. CONFIG_STACK_PROTECTOR to enable the stack protector feature by
   providing "-fstack-protector" compiler flag
2. CONFIG_STACK_PROTECTOR_STRONG to provide "-fstack-protector-strong"
3. CONFIG_STACK_PROTECTOR_ALL to provide "-fstack-protector-all"

Instead of fixing the compiler flag of stack-protector feature as
"-fstack-protector", we derive it from the introduced Kconfig
configurations. The compiler flag "stack-protector-cflags-y" is defined
as Makefile "immediately expanded variables" with ":=". Thus, the
stronger configuration of the stack protector can overwrite the
preceding one.

Signed-off-by: Alvin Chang <[email protected]>
Reviewed-by: Yu-Chien Peter Lin <[email protected]>
Reviewed-by: Anup Patel <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Anup Patel <[email protected]>

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