perf annotate: Split out read_symbol()

perf annotate: Split out read_symbol()

The Capstone disassembler code has a useful code snippet to read the
bytes for a given code symbol into memory. Split it out into its own
function, so that the LLVM disassembler can use it in the next patch.

Signed-off-by: Steinar H. Gunderson <sesse@google.com>
Cc: Ian Rogers <irogers@google.com>
Link: https://lore.kernel.org/r/20240803152008.2818485-2-sesse@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>