linux-user: Split out do_prctl and subroutines

linux-user: Split out do_prctl and subroutines

Since the prctl constants are supposed to be generic, supply
any that are not provided by the host.

Split out subroutines for PR_GET_FP_MODE, PR_SET_FP_MODE,
PR_GET_VL, PR_SET_VL, PR_RESET_KEYS, PR_SET_TAGGED_ADDR_CTRL,
PR_GET_TAGGED_ADDR_CTRL.  Return EINVAL for guests that do
not support these options rather than pass them on to the host.

Reviewed-by: Laurent Vivier <[email protected]>
Reviewed-by: Philippe Mathieu-Daudé <[email protected]>
Signed-off-by: Richard Henderson <[email protected]>
Message-Id: <20211227150127.2659293[email protected]>
Signed-off-by: Laurent Vivier <[email protected]>