Explicitly set cspace_size_bits in new processes

libsel4utils allows you to specify the size of a new processes cspace in
its interface. Relying on changing the library's default by changing the
value of LibSel4UtilsCSpaceSizeBits is much less flexible.

trivial: Style serial_server.c

Re-enable serial_server tests on RISC-V

These were disabled due to no platform user level serial driver existing
on any supported platforms. However as the serial server prints by
delegating to printf, these tests can still run correctly if printf is
using seL4_DebugPutChar internally.

riscv: add config_set guard to RISCV guards

SELFOUR-1280: conditionally run serial server tests

RISC-V has no serial device currently, so do not run these tests if the
architecture is RISC-V.

However, use the DEFINE_TEST macro, instead of #ifdef'ing out all of the
tests.

RISCV port

SELFOUR-1083 refactor tests because DEFINE_TEST_MAYBE was renamed to DEFINE_TEST

SELFOUR-1107 fix references to serial server
because serial server is now in a separate library

SELFOUR-1089 move serial server parent tests to libsel4utils

Add env argument to helper_set_priority, mcp

- it will be needed in future when SELFOUR-1016 is merged
- merge it now to avoid the conflicts inherent on a long running branch

Fix licenses

Use updated vka and allocman interfaces

The vka_utspace_alloc_at provides a much more reliable way of
retrieving a device frame capability, so we preference it
over using simple

Cast strlen to (int) in calls to test_eq

strlen returns a long and this is compared to error, which is an int.
There is no guarantee that these types are the same size (as required
by test_eq) and on x86_64 they actually different sizes

Increase allocman pool size

On x86_64 allocman needs a larger pool to bootstrap, this commit
increases the pool size to enable allocman to bootstrap (and these
tests to then pass) on x86_64

serial_server: add functionality tests

Add tests that determine the working status of the Serial Server
library under a range of reasonable conditions, both with a single
client and multiple clients. Tests the following under both single-user
and concurrent conditions:

* Connect to the server (from both the parent itself and other clients).
* Printf() and write()
* Connect, write some data, then disconnect, and reconnect and then write
some more data (connection reset/state diagram)
* Connect, disconnect and kill the server.

^ Use `make select-test TEST=SERSERV_CLIENT` to run the client thread tests.
^ Use `make select-test TEST=SERSERV_PARENT` to run the connection-from-parent
tests
^ Use `make select-test TEST=SERSERV_CLI_PROC` to run the client process
tests (these connect from a thread in a different VSpace and CSpace).
^ `make select-test TEST=SERSERV` will run all serial server tests.