dtc: Avoid UB when shifting

Prevent undefined behavior when shifting by a number that's bigger than
or equal to the width of the first operand.

Signed-off-by: Andrei Ziureaev <andrei.ziureaev@arm.com>
Message-Id: <20200714154542.18064-2-andrei.ziureaev@arm.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

dtc-parser.y

@@ -476,8 +476,8 @@ integer_rela:
 	;
 
 integer_shift:
-	  integer_shift DT_LSHIFT integer_add { $$ = $1 << $3; }
-	| integer_shift DT_RSHIFT integer_add { $$ = $1 >> $3; }
+	  integer_shift DT_LSHIFT integer_add { $$ = ($3 < 64) ? ($1 << $3) : 0; }
+	| integer_shift DT_RSHIFT integer_add { $$ = ($3 < 64) ? ($1 >> $3) : 0; }
 	| integer_add
 	;