cheri: elf: Setup per module RX and RW capabilities

cheri: elf: Setup per module RX and RW capabilities

The l_map_start and l_rw_start of the ld.so and exe comes from the auxv
since they are normally mapped by the kernel.  Some generic code had to
be modified so l_map_start is propagated and not overwritten when it is
recomputed.

The l_rw_range should exclude the relro region, but in libc.so and
ld.so this does not work: symbols are accessed before relro is applied
and then the permission should be writable.