yagl: Remove cur_ts global variable (1/3)

yagl: Remove cur_ts global variable (1/3)

cur_ts was a global variable used for easy global access to currently
running thread's state. Access to the variable was not synchronized at
all. The variable was overwritten each time a thread started working
and NULLed each time a thread stopped working. This was a cause
of multitude of multithreading issues in yagl code. Some examples are:
- Thread A could NULLify cur_ts after finishing work while thread B
tries to dereference it during logging routine setup. This in turn can
result in a randomly occuring segmentation fault (ex. when calling
YAGL_LOG_FUNC_ENTER which accessed cur_ts for PID/TID info).
- Information in cur_ts could be misleading for thread A because
thread B set its own instance of cur_ts right after thread A.
- Memory leaks and other issues due to cur_ts being re-allocated on the
same global pointer.

Issues have to be resolved by removing cur_ts. Now every thread based
function has a first parameter cur_ts, which provides the same information
in a per-thread and reentrant-safe manner.

In situations where cur_ts could not be reached (ex. initialization or
main thread code) YAGL_LOG_NO_TS macro was introduced, which for now sets
pid/tid information to 0. Macro's proper implementation will be done in
upcoming changes.

Some yagl modules also used local _ts structures (ex. egl_api_ts or
egl_onscreen_ts) and used them in the same way cur_ts was managed.
These also provide thread/reentry dangers and will be removed in
consecutive commits.

Change-Id: I9c55371a522d8f06cb3ce8120f88946e9d246695