soc: sam0: Add SERCOM fixup for samd5x

The SERCOMS on SAMD5x/SAME5x are connected to different MCLK
APBMASKs. There is no systematic way to tell whether a SERCOM
is connected to APBA, APBB, APBC or APBD, so rely on the
information from ASF instead of replicating it elsewhere.

This is needed for SPI, I2C and UART support on the SAMD5x/SAME5x
platform.

Signed-off-by: Benjamin Valentin <benjamin.valentin@ml-pa.com>