[BOLT][AArch64] Add support for SPE brstack format (#129231)

Since Linux 6.14, Perf gained the ability to report SPE branch events
using the `brstack` format, which matches the layout of LBR/BRBE.

This patch reuses the existing LBR parsing logic to support SPE.

Example SPE brstack format:
```bash
perf script -i perf.data -F pid,brstack --itrace=bl
```
```
  PID       FROM / TO / PREDICTED

16984  0x72e342e5f4/0x72e36192d0/M/-/-/11/RET/-
16984  0x72e7b8b3b4/0x72e7b8b3b8/PN/-/-/11/COND/-
16984  0x72e7b92b48/0x72e7b92b4c/PN/-/-/8/COND/-
16984  0x72eacc6b7c/0x760cc94b00/P/-/-/9/RET/-
16984  0x72e3f210fc/0x72e3f21068/P/-/-/4//-
16984  0x72e39b8c5c/0x72e3627b24/P/-/-/4//-
16984  0x72e7b89d20/0x72e7b92bbc/P/-/-/4/RET/-
```

SPE brstack flags can be two characters long: `PN` or `MN`:
- `P` = predicted branch
- `M` = mispredicted branch
- `N` = optionally appears when the branch is NOT-TAKEN
    - flag is relevant only to  conditional branches


Example of usage with BOLT:

1. Capture SPE branch events:
```bash
perf record -e 'arm_spe_0/branch_filter=1/u' -- binary
```

2. Convert profile for BOLT:
```bash
perf2bolt -p perf.data -o perf.fdata --spe binary
```

3. Run BOLT Optimization:
```bash
llvm-bolt binary -o binary.bolted --data   perf.fdata ...
```

A unit test verifies the parsing of the 'SPE brstack format'.

---------

Co-authored-by: Paschalis Mpeis <paschalis.mpeis@arm.com>

bolt/tools/driver/llvm-bolt.cpp

@@ -237,6 +237,13 @@ int main(int argc, char **argv) {
       if (Error E = RIOrErr.takeError())
         report_error(opts::InputFilename, std::move(E));
       RewriteInstance &RI = *RIOrErr.get();
+
+      if (opts::AggregateOnly && !RI.getBinaryContext().isAArch64() &&
+          opts::ArmSPE) {
+        errs() << ToolName << ": -spe is available only on AArch64.\n";
+        exit(1);
+      }
+
       if (!opts::PerfData.empty()) {
         if (!opts::AggregateOnly) {
           errs() << ToolName