Use R_MORELLO_RELATIVE for capabilility initialization in static executables

Instead of the __cap_relocs section, generate information needed for capability
initialisation in the .rela.dyn relocation section. The linker-generated
_rela_dyn{start,end} symbols mark the start/end of the .rela.dyn section. All
relocations are of type R_MORELLO_RELATIVE, which does not need any symbol
information; everything needed to initialise the capability is in the relocation
record and in the 128 bit fragment.

- Capability address: rela.r_offset
- Capability offset: rela.r_addend
- Capability base: fragbits<63:0>
- Capability size: fragbits<119:64>
- Capability permissions: fragbits<127:120>

This behavior is disabled by default and can be activated by the linker switch:
--morello-static-caps=elf