1. Removed function pointers for functions get_samples_per_slot(),
get_samples_slot_timestamp() and get_slot_from_timestamp() as it does
not offer any advantage. The functions are now called directly from
everywhere.
2. Optimized these functions by removing loops where ever possible.
Add two new functions for calculation symbol timestamp and symbol
duration for NR_DL_FRAME_PARMS. These functions are not using
the existing indirection mechanism via function pointers as this
prevents the compiler from properly optimizing the code.