kselftests: re-add ptp into main RDEPENDS
kselftests: re-add ptp into main RDEPENDS

Commit 371b7bb52225a3f7aadf57910aa9af3bf26c0e78 enabled ptp package, but
did not add it to RDEPENDS, fix it.

Signed-off-by: Denys Dmytriyenko <d29de71aea38aad3a87d486929cb0aad173ae612@ti.com>

rcn-ee/meta-ti,rcn-ee/meta-ti,rcn-ee/meta-ti,rcn-ee/meta-ti