s390/decompressor: swap .text and .rodata.compressed sections

.rodata.compressed section contains compressed linux image and is
quite large. By swapping text and rodata.compressed sections, the
decompressor code ends up between 0x11000 and 0x100000 addresses,
which makes it easier:
- to distinguish the decompressor phase from decompressed code (which
lives above 0x100000, except for small startup_continue),
- define break points which don't intersect with the main kernel image
later.

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