Initial v1.2.1 for Portenta_H7

### Initial Releases v1.2.1

1. Initial coding to support **Portenta_H7 boards** such as Portenta_H7 Rev2 ABX00042, etc., using [**ArduinoCore-mbed mbed_portenta** core](https://github.com/arduino/ArduinoCore-mbed)
2. Permit up to 16 super-long-time, super-accurate ISR-based timers to avoid being blocked
3. Using cpp code besides Impl.h code to use if Multiple-Definition linker error.
4. Bump version to v1.2.1 to sync with [STM32_TimerInterrupt library](https://github.com/khoih-prog/STM32_TimerInterrupt)

Author: khoih-prog

library.properties

@@ -3,7 +3,7 @@ version=1.2.1
 author=Khoi Hoang <[email protected]>
 maintainer=Khoi Hoang <[email protected]>
 sentence=This library enables you to use Interrupt from Hardware Timers on an STM32H7-based Portenta_H7 board
-paragraph=These Portenta_H7 Hardware Timers, using Interrupt, still work even if other functions are blocking. Moreover, they are much more precise (certainly depending on clock frequency accuracy) than other software timers using millis() or micros(). That's mandatory if you need to measure some data requiring better accuracy. It now supports 16 ISR-based Timers, while consuming only 1 Hardware Timer. Timers' interval is very long (ulong millisecs). The most important feature is they're ISR-based Timers. Therefore, their executions are not blocked by bad-behaving functions or tasks. This important feature is absolutely necessary for mission-critical tasks.
+paragraph=These Portenta_H7 Hardware Timers, using Interrupt, still work even if other functions are blocking. Moreover, they are much more precise (certainly depending on clock frequency accuracy) than other software timers using millis() or micros(). That's mandatory if you need to measure some data requiring better accuracy. It now supports 16 ISR-based Timers, while consuming only 1 Hardware Timer. Timers interval is very long (ulong millisecs). The most important feature is they're ISR-based Timers. Therefore, their executions are not blocked by bad-behaving functions or tasks. This important feature is absolutely necessary for mission-critical tasks.
 category=Device Control
 url=https://github.com/khoih-prog/Portenta_H7_TimerInterrupt
 architectures=mbed,mbed_portenta,ArduinoCore-mbed