platform/mellanox: mlxreg-hotplug: Add environmental data to uevent

Send "udev" event with environmental data in order to allow handling
"ENV{}" variables in "udev" rules.

Signed-off-by: Vadim Pasternak <vadimp@mellanox.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>