perf annotate-data: Handle RSP if it's not the FB register

perf annotate-data: Handle RSP if it's not the FB register

In some cases, the stack pointer on x86 (rsp = reg7) is used to point
variables on stack but it's not the frame base register.  Then it
should handle the register like normal registers (IOW not to access
the other stack variables using offset calculation) but it should not
assume it would have a pointer.

Before:
  -----------------------------------------------------------
  find data type for 0x7c(reg7) at tcp_getsockopt+0xb62
  CU for net/ipv4/tcp.c (die:0x7b5f516)
  frame base: cfa=0 fbreg=6
  no pointer or no type
  check variable "zc" failed (die: 0x7b9580a)
   variable location: base=reg7, offset=0x40
   type='struct tcp_zerocopy_receive' size=0x40 (die:0x7b947f4)

After:
  -----------------------------------------------------------
  find data type for 0x7c(reg7) at tcp_getsockopt+0xb62
  CU for net/ipv4/tcp.c (die:0x7b5f516)
  frame base: cfa=0 fbreg=6
  found "zc" in scope=3/3 (die: 0x7b957fc) type_offset=0x3c
   variable location: base=reg7, offset=0x40
   type='struct tcp_zerocopy_receive' size=0x40 (die:0x7b947f4)

Note that the type-offset was properly calculated to 0x3c as the
variable starts at 0x40.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20240412183310.2518474-5-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>