[S390] remove packed attribute from ext_int_info_t.

ext_int_info_t is no longer used in entry(64).S Instead do_extint is a C
function that handles the hash search.
As the structure is handled in C code, we can also remove the packed
attribute to avoid alignment issues. (Currently there is no alignment
problem in ext_int_info_t, even if packet)

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>