s390/vdso: add .got.plt in vdso linker script

KCFLAGS="-mno-pic-data-is-text-relative" make leads to bfd assertion
error in s390_got_pointer():

LD      arch/s390/kernel/vdso64/vdso64.so.dbg
ld: BFD version 2.35-18.fc33 assertion fail elf-s390-common.c:74

readelf -Wr vdso64_generic.o | grep GOT
0000000000000032  000000110000001a R_390_GOTENT 0000000000000000 _vdso_data + 2
(...)

Add .got.plt in linker script to avoid this.

Suggested-by: Ilya Leoshkevich <iii@linux.ibm.com>
Signed-off-by: Sumanth Korikkar <sumanthk@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>