Unified gpio_t structure PinName field name to 'pin'

Added simple indexing operator in KPSDK_MCUS target hal for BusOut component in mbed SDK

DigitalOut now has simple interface to obtain Pinname directly from gpio_t (via unified PInaName 'pin' field in structure
Unified gpio_t structure PinName field name to 'pin'

Added simple indexing operator in KPSDK_MCUS target hal for BusOut component in mbed SDK

DigitalOut now has simple interface to obtain Pinname directly from gpio_t (via unified PInaName 'pin' field in structure
Added unit tests for BusOut with new improvements