i2c: thunderx: Replace pci_enable_msix()

Using pci_alloc_irq_vectors() instead of the deprecated
pci_enable_msix() allows to remove the msix_entry from
struct octeon_i2c and thus to get rid of the config symbol check.

Signed-off-by: Jan Glauber <jglauber@cavium.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>