s390/decompressor: discard __ksymtab and .eh_frame sections

__ksymtab sections created for exported symbols are not needed
during the decompressor phase and could be discarded to save the memory.
The source of those exports is ebcdic.o, which is linked into both
vmlinux and boot/compressed/vmlinux.

.eh_frame section is also unused and could be discarded from
boot/compressed/vmlinux. The same has been done for vmlinux in:
"s390/kernel: emit CFI data in .debug_frame and discard .eh_frame
sections".

Signed-off-by: Vasily Gorbik <gor@linux.vnet.ibm.com>
Reviewed-by: Hendrik Brueckner <brueckner@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>