time/clock_gettime: add handling of CLOCK_THREAD_CPUTIME_ID flag

[R4ken]

JIRA: RTOS-1088

Description

Add handling of missing CLOCK_THREAD_CPUTIME_ID flag in clock_gettime function.
This allows apps to know how much time did a thread spend on a CPU.

Motivation and Context

Missing functionality useful for porting apps

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Chore (refactoring, style fixes, git/CI config, submodule management, no code logic changes)

How Has This Been Tested?

• Already covered by automatic testing.
• New test added: (add PR link here).
• Tested by hand on: (ia32-generic-qemu, armv7a9-zynq7000-qemu)

Checklist:

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing linter checks and tests passed.
• My changes generate no new compilation warnings for any of the targets.

Special treatment

• This PR needs additional PRs to work:
  • syscalls: implement getThreadCpuTime syscall phoenix-rtos-kernel#692
• I will merge this PR by myself when appropriate.

[oI0ck]

LGTM

[oI0ck]

Merge after phoenix-rtos/phoenix-rtos-kernel#692