Introduce __rseq_cs_ptr_array, rename __rseq_table to __rseq_cs

Introduce __rseq_cs_ptr_array, rename __rseq_table to __rseq_cs

The entries within __rseq_table are aligned on 32 bytes due to
linux/rseq.h struct rseq_cs uapi requirements, but the start of the
__rseq_table section is not guaranteed to be 32-byte aligned. It can
cause padding to be added at the start of the section, which makes it
hard to use as an array of items by debuggers.

Considering that __rseq_table does not really consist of a table due to
the presence of padding, rename this section to __rseq_cs.

Create a new __rseq_cs_ptr_array section which contains 64-bit packed
pointers to entries within the __rseq_cs section.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>