rtl872x: revert the flash speed to 80MHz

[YutingYou]

Problem

This is a mistake I made in PR2470

The older datasheet indicates support for QSPI speeds of up to 60MHz, whereas the newer one indicates support for speeds of up to 80MHz.

Realtek also tested MX25R32 with 80MHz speed:

UM0404 Ameba Flash AVL-EN_20210621(45695).pdf
MX25R6435F v0.03.pdf
MX25R6435F v1.6.pdf

Solution

Revert the flash speed from 57MHz to 80MHz.

NOTE: This PR requires updating the prebootloader-part1!

Steps to Test

1. Update the prebootloader to observe the flash clock with an oscilloscope
2. Update prebootloader with the change in this PR, use bootloader/system-part without this changeset
3. Update bootloader
4. Update system-part

References

N/A

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Completeness

• User is totes amazing for contributing!
• Contributor has signed CLA (Info here)
• Problem and Solution clearly stated
• Run unit/integration/application tests on device
• Added documentation
• Added to CHANGELOG.md after merging (add links to docs and issues)

[YutingYou]

Test result with oscilloscope

Cross version test on DVOSv5.4.0

# Download vesion v5.4.0
device-os-flash --all-devices 5.4.0

# Update prebootboader-mbr
particle flash --serial prebootloader-part1-80MHz.bin

# Update user app, then it will trigger safe mode to update bootloader and system-part1
particle flash --usb /Users/yuting/Desktop/blank-80MHz-PR.bin

blank-80MHz-PR.bin.zip
prebootloader-part1-80MHz-PR.bin.zip