bios: Fix build when ethphy is present but ethmac is not.

While testing my Ethernet DMA, I renamed the `ethmac` module to `ethmac_dma` so that it wouldn't be used from the BIOS, but I got an undefined reference to `eth_init` because `bios.c` checks different CSR defines than the code that defines `eth_init`.

boards/arty : Add directly connected spi clk pin 

Imported from LiteICLink. PRBS can be useful for different purposes, so is
better integrated in LiteX.

When running OS with LiteX and when LiteXTerm is use, we want to be able to
send CTRl-C to the OS. Ensure a specific sequence is sent to close the terminal.

In most of the case, execution speed is already fast enough with -O0 and
with complex design -O0 is a lost faster to compile than -O3. In the future
we could add a switch to choose which optimization we want.

De10lite support

Extend generated headers & csv

For some FPGAs (e.g. MAX10) .rbf file cannot be generated.
Add possibility to turn off that feature for those chips.

software/libbase: memcpy: simple, arch-width agnostic implementation

Remove optimizations targeted specifically at rv32 architecture,
allowing memcpy to work on all word sizes.

Since this is "only" the BIOS, it is also arguably better to
optimize for size rather than performance, given that control
will be quickly handed over to some other program being loaded.
Signed-off-by: Gabriel Somlo <gsomlo@gmail.com>

fix signed char type to be explicitly signed

needed for some third party libraries to compile

Fix interrupt_name in soc_core/add_interrupt

Add support for Terasic DE2-115 and Terasic DE1-SoC boards