I just called Apple for help on this, as I also have an Enterprise account and no longer see this option. They actually had to manually enable my account as an MDM provider account. Once they did this, I went into certificates, identifiers and profiles ---> IOS certificates and clicked the plus sign (+) to create a new certificate. Now that they have activated "MDM vendorship" in my account, there is a new switch in the Production section called "MDM CSR" where I can create a new MDM certificate.
Hope this helps!
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