arm64: entry.S: convert elX_irq

Following our 'dai' order, irqs should be processed with debug and
serror exceptions unmasked.

Add a helper to unmask these two, (and fiq for good measure).

Signed-off-by: James Morse <james.morse@arm.com>
Reviewed-by: Julien Thierry <julien.thierry@arm.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

arch/arm64/include/asm/assembler.h

@@ -55,6 +55,11 @@
 	msr	daif, \tmp
 	.endm
 
+	/* IRQ is the lowest priority flag, unconditionally unmask the rest. */
+	.macro enable_da_f
+	msr	daifclr, #(8 | 4 | 1)
+	.endm
+
 /*
  * Enable and disable interrupts.
  */