[CHG]dlelf.c support distinguishing 32-bit ELF format and 64-bit ELF format

Use `rt_thread_self()` to determine whether the scheduler is started or not.

Try a few times before switching to other data widths. 
The original strategy (simply wait for 20ms ) failed on STM32H743 with an MTFC4GACAJCN-4M (4GB EMMC) when switching data width. 
(unless the debugging info is enabled, which add more delays)
With this EMMC, the fixed delay was set to 50ms for it to be able to work. 

Instead of a fixed delay, I think we better change to trying a few more times with smaller delays.

Signed-off-by: Nyuanjie <yuanjie@rt-thread.com>