nvmem: imx-ocotp: Elongate OCOTP_CTRL ADDR field to eight bits
i.MX6 defines OCOTP_CTRLn:ADDR as seven bit address-field with a one bit
RSVD0 field, i.MX7 defines OCOTP_CTRLn:ADDR as a four bit address-field
with a four bit RSVD0 field.
i.MX8 defines the OCOTP_CTRLn:ADDR bit-field as a full range eight bits.
i.MX6 and i.MX7 should return zero for their respective RSVD0 bits and
ignore a write-back of zero where i.MX8 will make use of the full range.
This patch expands the bit-field definition for all users to eight bits,
which is safe due to RSVD0 being a no-op for the i.MX6 and i.MX7.