Higher clock speed SPI/I2C

[mcserved]

Summary:

The clock speeds for both the I2C and SPI interface were made more configurable and clear. Only I2C device that could not handle 300 kHz was the secure element. These apps were tested and worked normally: basic, basic_lorawan, freefall_lorawan. Speeds were calculated with STM32CubeMX and tested afterwords with a logic analyzer. Closes #39.

Changes:

• Increased the speeds for I2C and SPI to their functional maximum
• Added more defines for the I2C clock speeds
• SPI clock speeds were documented better

[mcserved]

I haven't tested this yet, but I plan to, did you try one of these configurations with the basic_lorawan app?

I've tested with freefall_lorawan, which is basically the same (+ it uses the I2C for the accelerometer). I tested just now to be sure and it seemed to work as usual.