el0_sync also unmasks exceptions on a case-by-case basis, debug exceptions
are enabled, unless this was a debug exception. Irqs are unmasked for
some exception types but not for others.

el0_dbg should run with everything masked to prevent us taking a debug
exception from do_debug_exception. For the other cases we can unmask
everything. This changes the behaviour of fpsimd_{acc,exc} and el0_inv
which previously ran with irqs masked.

This patch removed the last user of enable_dbg_and_irq, remove it.
Signed-off-by: NJames Morse <james.morse@arm.com>
Reviewed-by: NJulien Thierry <julien.thierry@arm.com>
Reviewed-by: NCatalin Marinas <catalin.marinas@arm.com>
Signed-off-by: NWill Deacon <will.deacon@arm.com>