Refactor sleep tracing driver identifier to be pointer to the driver filepath.
Refactor sleep tracing driver identifier to be pointer to the driver filepath.

The use of __FILE__ macro to get a usable identifier from the driver path
causes the path of the file to be stored in the .text region of the binary.
Given that this remains for the entire duration of the program, storing a
pointer to this string as an identifier is more efficient than copying the
contents of the string during lookup/insertion.
andcor02/mbed-os,betzw/mbed-os,mbedmicro/mbed,betzw/mbed-os,betzw/mbed-os,andcor02/mbed-os,mbedmicro/mbed,kjbracey-arm/mbed,c1728p9/mbed-os,c1728p9/mbed-os,betzw/mbed-os,mbedmicro/mbed,c1728p9/mbed-os,mbedmicro/mbed,c1728p9/mbed-os,betzw/mbed-os,kjbracey-arm/mbed,betzw/mbed-os,andcor02/mbed-os,c1728p9/mbed-os,andcor02/mbed-os,mbedmicro/mbed,andcor02/mbed-os,kjbracey-arm/mbed,c1728p9/mbed-os,kjbracey-arm/mbed,andcor02/mbed-os