Fix uvisor ticker issue on K64F

[orenc17]

Description

Restore lp_ticker_free to previous implementation
This fixes uvisor tests on K64F
This is a temporary patch until uvisor is removed

Pull request type

[x] Fix
[ ] Refactor
[ ] Target update
[ ] Functionality change
[ ] Breaking change

[0xc0170]

/morph build

[0xc0170]

As this functionality is will be reverted once uvisor removal lands, this shall be fine as long as it fixes the issue

[mbed-ci]

Build : SUCCESS

Build number : 2837
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/7830/

Triggering tests

/morph test
/morph uvisor-test
/morph export-build
/morph mbed2-build

[0xc0170]

The device in uvisor CI timeouts , please review

[mbed-ci]

Test : SUCCESS

Build number : 2588
Test logs :http://mbed-os-logs.s3-website-us-west-1.amazonaws.com/?prefix=logs/7830/2588

[0xc0170]

The device in uvisor CI timeouts , please review

From what I can tell, fails to sync with the device (fails to allocate or ?). cc @OPpuolitaival

[mbed-ci]

Exporter Build : SUCCESS

Build number : 2465
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/exporter/7830/

[0xc0170]

/morph uvisor-test