arch/tricore: Improve up_backtrace implementation

[zyfeier]

Summary

Improve the existing TriCore up_backtrace() implementation (merged in #18899):

1. Conditional compilation — Make tricore_backtrace.c conditional on CONFIG_SCHED_BACKTRACE, consistent with RISC-V and ARM architectures.
2. NULL return address check — Terminate backtrace early when csa[REG_UA11] == 0 to avoid invalid entries.
3. Fix non-current task backtrace — Use regs[REG_LPCXI] instead of tricore_addr2csa(tcb->xcp.regs) to preserve the UL bit needed for correct CSA type identification.

Testing

Verified on TC4D9 EVB (triboard_tc4x9_com:nsh) with CONFIG_SCHED_BACKTRACE=y:

• ostest passes completely (Exiting with status 0)
• Triggered PANIC() in hello app, backtrace output:

sched_dumpstack: backtrace| 4: 0x80028be4 0x80024650 0x800141b0 0x800144aa 0x800115d0 0x80011570

addr2line verification:

0x80028be4 → sched_dumpstack (libs/libc/sched/sched_dumpstack.c:71)
0x80024650 → dump_assert_info (sched/misc/assert.c:727)
0x800141b0 → __assert (libs/libc/assert/lib_assert.c:39)
0x800144aa → nxtask_startup (libs/libc/sched/task_startup.c:72)
0x800115d0 → nxtask_start (sched/task/task_start.c:72)
0x80011570 → nxtask_start (sched/task/task_start.c:70)

Call chain is correct. User-space functions (hello_main/func_a/func_b/func_c) are not in backtrace because the compiler optimized them into tail-jumps (j instead of call), which is expected TriCore behavior — only call instructions save Upper CSA.

[xiaoxiang781216]

@zyfeier please fix the conflict