tracing_user: Add ISR nest level parameter

For tracing_user, the sys_trace_isr_enter() & sys_trace_isr_exit()
block any nest interrupts & most SMP interrupts for the user. It is
hard to analyze the IRQ preemption(e.g., each IRQ counter and execution
time). This commit adds ISR nest level for each CPU to the user instead
of blocking user call back when nest interrupts.

Signed-off-by: Wealian Liao <WHLIAO@nuvoton.com>