load_elf: Remove unused address variables from callers

Several callers of load_elf() pass pointers for lowaddr and highaddr
parameters which are then not used for anything. This may stem from a
misunderstanding that load_elf need a value here but in fact it can
take NULL to ignore these values. Remove such unused variables and
pass NULL instead from callers that don't need these.

Signed-off-by: BALATON Zoltan <balaton@eik.bme.hu>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Acked-by: David Gibson <david@gibson.dropbear.id.au>
Acked-by: Max Filippov <jcmvbkbc@gmail.com>
Message-Id: <20200705174020.BDD0174633F@zero.eik.bme.hu>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>