sysui: bump perfetto shmem buffer size to 1 MB

Increase Perfetto's shmem buffer from to 512 KB to 1 MB.

We observed that sysui can have >100 threads which is close
to the limit imposed by the current buffer size:
512KB -> 128 chunks -> max 128 threads writing to perfetto

Bug: b/420587648
Flag: android.tracing.sysui_large_perfetto_shmem_buffer
Test: presubmit
Change-Id: I745468b3296cd0e15896468d4687abc62bb92852