net: make caching calls work on RISC-V, even though they are no-ops

Rather than having #ifdefs for ARM, we instead have the implementations
handle the architecture specific operations. In RISC-V's case, this is
just a no-op.

I removed `ROUND_UP(buffer.len, 1 << CONFIG_L1_CACHE_LINE_SIZE_BITS)`
because we do the rounding up in `cache_clean_and_invalidate`
anyways. We can't have this line on RISC-V because
`CONFIG_L1_CACHE_LINE_SIZE_BITS` does not exist on non-ARM architectures.

Signed-off-by: Ivan Velickovic <i.velickovic@unsw.edu.au>

network/components/virt_rx.c

@@ -93,15 +93,7 @@ void rx_return(void)
             // Cache invalidate after DMA write, so we don't read stale data.
             // This must be performed after the DMA write to avoid reading
             // data that was speculatively fetched before the DMA write.
-            //
-            // We would invalidate if it worked in usermode. Alas, it
-            // does not -- see [1]. The fastest operation that works is a
-            // usermode CleanInvalidate (faster than a Invalidate via syscall).
-            //
-            // [1]: https://developer.arm.com/documentation/ddi0595/2021-06/AArch64-Instructions/DC-IVAC--Data-or-unified-Cache-line-Invalidate-by-VA-to-PoC
-            #ifdef CONFIG_ARCH_ARM
-            cache_clean_and_invalidate(buffer_vaddr, buffer_vaddr + ROUND_UP(buffer.len, 1 << CONFIG_L1_CACHE_LINE_SIZE_BITS));
-            #endif
+            cache_clean_and_invalidate(buffer_vaddr, buffer_vaddr + buffer.len);
             int client = get_mac_addr_match((struct ethernet_header *) buffer_vaddr);
             if (client == BROADCAST_ID) {
                 int ref_index = buffer.io_or_offset / NET_BUFFER_SIZE;

network/components/virt_tx.c

@@ -62,10 +62,8 @@ void tx_provide(void)
                     assert(!err);
                     continue;
                 }
-                #ifdef CONFIG_ARCH_ARM
                 cache_clean(buffer.io_or_offset + state.buffer_region_vaddrs[client],
                             buffer.io_or_offset + state.buffer_region_vaddrs[client] + buffer.len);
-                #endif
 
                 buffer.io_or_offset = buffer.io_or_offset + state.buffer_region_paddrs[client];
                 err = net_enqueue_active(&state.tx_queue_drv, buffer);