staging: et131x: Remove last of the forward declarations

Moved functions in et131x.c file to remove the forward declarations of:

et131x_rx_dma_disable
et131x_rx_dma_enable
et131x_init_send
et131x_tx_dma_enable

Signed-off-by: Mark Einon <mark.einon@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>