net: stmmac: make dma_cfg mixed/fixed burst boolean

net: stmmac: make dma_cfg mixed/fixed burst boolean

struct stmmac_dma_cfg mixed_burst/fixed_burst members are both boolean
in nature - of_property_read_bool() are used to read these from DT, and
they are only tested for non-zero values. Use bool to avoid unnecessary
padding in this structure.

Update dwmac-intel to initialise these using true rather than '1', and
remove the '0' initialisers as the struct is already zero initialised
on allocation.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Link: https://patch.msgid.link/E1vvuXn-0000000AvnX-4A1u@rmk-PC.armlinux.org.uk
Signed-off-by: Jakub Kicinski <kuba@kernel.org>