s390/boot: sanitize kaslr_adjust_relocs() function prototype

Do not use vmlinux.image_size within kaslr_adjust_relocs() function
to calculate the upper relocation table boundary. Instead, make both
lower and upper boundaries the function input parameters.

Acked-by: Sumanth Korikkar <sumanthk@linux.ibm.com>
Acked-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>