ixgbe: fix semaphores in eeprom routines for x540

HW can upload EEPROM content from flash while
in a middle of checksum calculation. Take NVM ownership for the whole
process of checksum update.

Call ixgbe_read_eerd_generic() and ixgbe_write_eewr_generic() directly to
avoid double take of semaphores which leads to long loading times.

Signed-off-by: Emil Tantilov <emil.s.tantilov@intel.com>
Tested-by: Stephen Ko <stephen.s.ko@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>