Documentation: Fix incorrect timer initialization API names

[arnavsharma990]

Note: Please adhere to Contributing Guidelines.

Summary

*The tickless OS documentation contains incorrect names for the
platform timer initialization APIs.

This change corrects up_timer_intialize() to
up_timer_initialize() and up_intialize() to up_initialize(),
matching the API declarations in include/nuttx/arch.h.*

Impact

Documentation-only change.

Testing

make html

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Pure documentation changes can just be tested with make html
(see docs) and verification of the correct format in your
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request test logs.

[Abhishekmishra2808]

Thanks @arnavsharma990. Follow the contribution guidelines (https://nuttx.apache.org/docs/latest/contributing/guide.html), 1. Sign the commit msg
2. The commit msg should contain a description of the changes

[arnavsharma990]

@Abhishekmishra2808 Thank you for pointing this out. I have updated the commit to include the required signature and a detailed description of the changes, in accordance with the NuttX contribution guidelines.

The updated commit has been pushed to the PR.