arm64: Enable interrupts in the EL0 undef handler

do_undefinstr() has to be called with interrupts disabled since it may
read the instruction from the user address space which could lead to a
data abort and subsequent might_sleep() warning in do_page_fault().

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/kernel/entry.S

@@ -476,6 +476,8 @@ el0_undef:
 	 * Undefined instruction
 	 */
 	mov	x0, sp
+	// enable interrupts before calling the main handler
+	enable_irq
 	b	do_undefinstr
 el0_dbg:
 	/*