rpi: mkimage: Make the image large enough for future additions

Change the image size from 256 MiB to 512 MiB in order to have enough room left
for future additions.

Signed-off-by: Benoît Thébaudeau <benoit.thebaudeau@advansee.com>
rpi: linux: crypto: Enable ARM optimizations

Signed-off-by: Benoît Thébaudeau <benoit.thebaudeau@advansee.com>
rpi: linux: crypto: Enable SHA512

Signed-off-by: Benoît Thébaudeau <benoit.thebaudeau@advansee.com>
rpi: linux: crypto: Enable userspace configuration

Signed-off-by: Benoît Thébaudeau <benoit.thebaudeau@advansee.com>
rpi: Add support for audio

Signed-off-by: Benoît Thébaudeau <benoit.thebaudeau@advansee.com>
rpi-userland: Fix vcfiled startup test

`S97vcfiled start` used start-stop-daemon with --start and --test in order to
detect whether the daemon had already been started. However, contrary to
Debian's start-stop-daemon, BusyBox's does not support --test with --start, but
only with --stop, so change this test to use --stop instead.

Signed-off-by: Benoît Thébaudeau <benoit.thebaudeau@advansee.com>
dhcpdump: Fix strsep() feature test

Use the official _BSD_SOURCE feature test macro instead of the meaningless
HAVE_STRSEP macro in order to detect the availability of strsep().

This allows toolchains supporting strsep() to use it instead of the custom
implementation from dhcpdump, which also avoids the following error with some
toolchains:

  In file included from dhcpdump.c:30:0:
  dhcpdump.c: At top level:
  strsep.c:65:23: error: register name not specified for ‘delim’
    register const char *delim;
                         ^

Signed-off-by: Benoît Thébaudeau <benoit.thebaudeau@advansee.com>
rpi: Enable many useful features and packages

Signed-off-by: Benoît Thébaudeau <benoit.thebaudeau@advansee.com>
README.md: Add the boot time

Signed-off-by: Benoît Thébaudeau <benoit.thebaudeau@advansee.com>