Optimize flash writes on SAMD51

[mateusznowakdev]

Related to #4905, this PR will apply similar change to SAMD51, switching from write-quad to write-page mode.

https://ww1.microchip.com/downloads/en/DeviceDoc/SAM_D5xE5x_Family_Data_Sheet_DS60001507F.pdf
section 9.2.1 says

A single page contains 512 Bytes, which is applicable to all the device part numbers listed in the Configuration Summary

[deadprogram]

Appears to work as expected:

$ tinygo flash -target pybadge -monitor examples/flash
Connected to /dev/ttyACM0. Press Ctrl-C to exit.
Flash data start:       0x00008000
Flash data end:         0x00080000
Flash data size, bytes: 491520
Flash write block size: 512
Flash erase block size: 8192

Reading original data from flash:
1234567887654321123456788765432112345678876543211234567887654321123456788765432112345678876543211234567887654321123456788765432112345678876543211234567887654321123456788765432112345678876543211234567887654321123456788765432112345678876543211234567887654321
Erasing flash...
Writing new data to flash:
1234567887654321123456788765432112345678876543211234567887654321123456788765432112345678876543211234567887654321123456788765432112345678876543211234567887654321123456788765432112345678876543211234567887654321123456788765432112345678876543211234567887654321
Reading data back from flash: 
1234567887654321123456788765432112345678876543211234567887654321123456788765432112345678876543211234567887654321123456788765432112345678876543211234567887654321123456788765432112345678876543211234567887654321123456788765432112345678876543211234567887654321
Done.

Thank you for working on this @mateusznowakdev now merging.