net: stmmac: move stmmac_axi_blen_to_mask() to stmmac_main.c

net: stmmac: move stmmac_axi_blen_to_mask() to stmmac_main.c

Move the call to stmmac_axi_blen_to_mask() out of the individual
MAC version drivers into the main code in stmmac_init_dma_engine(),
passing the resulting value through a new member, axi_blen_regval,
in the struct stmmac_axi structure.

There is now no need for stmmac_axi_blen_to_dma_mask() to use
u32p_replace_bits(), so use FIELD_PREP() instead.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Link: https://patch.msgid.link/E1vLfLW-0000000FMb1-0zKV@rmk-PC.armlinux.org.uk
Signed-off-by: Jakub Kicinski <kuba@kernel.org>