ArmPlatformPkg: Update LcdHwNullLib to Prevent Init

[os-d]

Description

Library previously returned EFI_SUCCESS which causes the platform to continue initializing LCD HW. Should return EFI_NOT_FOUND as this is a null library.

Resolves TCBZ3351: https://bugzilla.tianocore.org/show_bug.cgi?id=3351.

• [ ] Breaking change?
  • Breaking change - Does this PR cause a break in build or boot behavior?
  • Examples: Does it add a new library class or move a module to a different repo.
• [ ] Impacts security?
  • Security - Does this PR have a direct security impact?
  • Examples: Crypto algorithm change or buffer overflow fix.
• [ ] Includes tests?
  • Tests - Does this PR include any explicit test code?
  • Examples: Unit tests or integration tests.

How This Was Tested

Tested using the null lib and seeing LCD HW init not continue.

Integration Instructions

N/A.

[os-d]

@ardbiesheuvel @leiflindholm @samimujawar can you please review?