Network: add AWS Elastic Network Adapter (ENA) driver

This adds nework connectivity to AWS Nitro instances (KVM-based).
The code is derived from the Amazon ENA driver for FreeBSD
(https://github.com/amzn/amzn-drivers/blob/master/kernel/fbsd/ena).
Tested on t3, t3a, c4, c5, c5a, c5d and c5n instances.

Closes #1233.

platform/pc/Makefile

@@ -5,6 +5,10 @@ PROGRAMS=	kernel.img
 SRCS-kernel.img= \
 	$(CURDIR)/service.c \
 	$(OBJDIR)/gitversion.c \
+	$(SRCDIR)/aws/ena/ena.c \
+	$(SRCDIR)/aws/ena/ena_com/ena_com.c \
+	$(SRCDIR)/aws/ena/ena_com/ena_eth_com.c \
+	$(SRCDIR)/aws/ena/ena_datapath.c \
 	$(SRCDIR)/drivers/ata.c \
 	$(SRCDIR)/drivers/ata-pci.c \
 	$(SRCDIR)/drivers/console.c \

platform/pc/service.c

@@ -11,6 +11,7 @@
 #include <storage.h>
 #include <symtab.h>
 #include <unix.h>
+#include <aws/aws.h>
 #include <virtio/virtio.h>
 #include <vmware/vmxnet3.h>
 #include <drivers/acpi.h>
@@ -533,6 +534,7 @@ static void __attribute__((noinline)) init_service_new_stack()
         /* qemu virtio */
         init_virtio_network(kh);
         init_vmxnet3_network(kh);
+        init_aws_ena(kh);
     }
 
     init_storage(kh, sa, !xen_detected() && !hyperv_storvsc_attached);

src/aws/aws.h

@@ -0,0 +1 @@
+void init_aws_ena(kernel_heaps kh);