xtensa: add config option to disable linker relaxation

The default linker behavior is to optimize identical literal values and
remove unnecessary overhead from assembler-generated "longcall" sequences
to reduce code size. Provide an option to disable this behavior to improve
compile time.

Signed-off-by: Chris Zankel <chris@zankel.net>

diff --cc arch/xtensa/Kconfig.debug
Simple merge

diff --cc arch/xtensa/Makefile
Simple merge