package/gcc: xtensa: fix atomic NAND code generation

xtensa gcc incorrectly generates code for atomic NAND operation as
~a1 & a2 instead of ~(a1 & a2). Fix that.

Backported from: r264087
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>