arm64: kernel: do not need to reset UAO on exception entry

Commit e19a6ee2 ("arm64: kernel: Save and restore UAO and
addr_limit on exception entry") states that exception handler inherits
the original PSTATE.UAO value, so UAO needes to be reset
explicitly. However, ARM 8.2 Extension documentation says:

PSTATE.UAO is copied to SPSR_ELx.UAO and is then set to 0 on an
exception taken from AArch64 to AArch64

so hardware already does the right thing.
Signed-off-by: Vladimir Murzin <vladimir.murzin@arm.com>
Acked-by: James Morse <james.morse@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

arch/arm64/kernel/entry.S

@@ -104,7 +104,7 @@
 	str	x20, [sp, #S_ORIG_ADDR_LIMIT]
 	mov	x20, #TASK_SIZE_64
 	str	x20, [tsk, #TI_ADDR_LIMIT]
-	ALTERNATIVE(nop, SET_PSTATE_UAO(0), ARM64_HAS_UAO, CONFIG_ARM64_UAO)
+	/* No need to reset PSTATE.UAO, hardware's already set it to 0 for us */
 	.endif /* \el == 0 */
 	mrs	x22, elr_el1
 	mrs	x23, spsr_el1