Set Serial Clockrate based on data parsed from host firmware

[MrChromebox]

Description

Set PcdSerialClockRate from SerialPortInfo in UefiPayloadEntry.

The initial approach was to add a ClockRate field to UNIVERSAL_PAYLOAD_SERIAL_PORT_INFO data struct, but simplified to setting the PCD directly based on feedback from reviewers.

These changes enable the serial clock rate value, which is already passed in from the host firmware, to be used when configuring the serial port for debug output. AMD Zen platform devices require this in order to have functional serial output.

• Breaking change?
• Impacts security?
• Includes tests?

How This Was Tested

build/boot multiple AMD/Intel devices and verify serial output works for all.

Integration Instructions

N/A

[vbpandya]

stating the obvious caught by CI :)
"WARNING - Line 3 of commit message is too long (76 >= 76)"

[gguo11837463]

Before make this change, please make sure this document got update.
https://universalscalablefirmware.github.io/documentation/2_universal_payload.html

Header Revision should be changed from 1 to 2.
Header Length should be change from 18 to 22.

Source Code should be change like below.
if (SerialPortInfo->Header.Revision >= 1) {
XXX
}

[MrChromebox]

@gguo11837463 have opened a PR to update the documentation here:
UniversalScalableFirmware/documentation#61

Will update this PR to only use the ClockRate if header version >= 2.