fdt_support: Fixup 'ethernet' aliases not ending in digits

The Raspberry Pi device tree files since Linux v4.9 have a "ethernet"
alias pointing to the on-board Ethernet device node. However,
U-Boot's fdt_fixup_ethernet() only looks at ethernet aliases ending
in digits.

As the spec doesn't mandate that aliases must end in numbers and there
have been much older uses of an "ethernet" aliases in the wild
(according to Tom Rini), change the code to accept "ethernet" as well.

Without this Linux isn't told of the MAC address provided by the
RPI firmware and the ethernet interface is always assigned a random MAC
address.

Signed-off-by: Tuomas Tynkkynen <tuomas@tuxera.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>