This is the only drivers that AMD Download page has for your Embedded AMD Processor but only for Ubuntu Linux: https://www.amd.com/en/support/embedded/amd-embedded-radeon/amd-embedded-e-series/e8860
You can open a AMD Support ticket and ask them if they have an updated RHEL 7.5 driver for your embedded processor from here: https://www.amd.com/en/support/contact-email-form
EDIT: Found this Redhat thread concerning driver for the AMD E8860 from Redhat Linux website: https://access.redhat.com/discussions/4771321
It mentions the RHEL provides native AMD drivers for your Embedded processor. So see if your RHEL 7.5 native drivers works with your processor or not.
If not the Users suggest using a 3rd party driver.