[driverctl] Add "warn" log level

Change-Id: I12ff68531e5763f0724a1e20323045acd767c2f5

[ddk][driverctl] Add ioctl and driverctl tool manipulating driver log flags

Usage: driverctl <path> <command> [options]

where path is path to driver file in /dev

Command "log":
options are zero or more of:
"error" or "e": DDK_LOG_ERROR
"info" or "i": DDK_LOG_INFO
"trace" or "t": DDK_LOG_TRACE
"spew" or "s": DDK_LOG_SPEW
"debug1" or "d1": DDK_LOG_DEBUG1
"debug2" or "d2": DDK_LOG_DEBUG2
"debug3" or "d3": DDK_LOG_DEBUG3
"debug4" or "d4": DDK_LOG_DEBUG4

With no options provided, driverctl log will print the current log flags for the driver.
A flag may have a '+' or '-' prepended. In that case the flag will be toggled
on (+) or off(-) without affecting other flags.
If toggled flags are used, all flags must be toggled.

Examples:

Set log flags to DDK_LOG_ERROR | DDK_LOG_INFO | DDK_LOG_TRACE:
$ driverctl <path> log error info trace
or:
$ driverctl <path> log e i t

Turn on DDK_LOG_TRACE and DDK_LOG_SPEW:
$ driverctl <path> log +trace +spew
or:
$ driverctl <path> log +t +s

Turn off DDK_LOG_SPEW:
$ driverctl <path> log -spew
or:
$ driverctl <path> log -s

Change-Id: Icbf1a6e45dcfa8b2dea21f9d2199d5283842cf7b