simpleperf: scripts: Fix using vmlinux in symfs_dir

When reporting using scripts, simpleperf doesn't use vmlinux
for kernel symbolization if we set record file before symfs_dir.
Because simpleperf creates KernelDso when setting record file.
And KernelDso finds debug file path in its constructor.

To fix this, let KernelDso find debug file path when needed. That's
after setting symfs_dir.

Bug: 304815072
Test: run simpleperf_unit_test
Test: run test.py -p TestReportLib.test_use_vmlinux
Change-Id: Ib0a6de55e66562f271de10b985af867f2e10f61f
4 files changed