[include][console] split lib/console.h into two

TL;DR most uses of lib/console.h -> lk/console_cmd.h

Move the part that lets a piece of code somewhere in the system to
define a console command from the actual lib/console api to start an
instance of the console. Move in almost every place the user of the
console command definition to the new header, lk/console_cmd.h which is
always in the include path.

Also remove most uses of testing for WITH_LIB_CONSOLE since you can
almost always just safely define it and then let the linker remove it.

app/loader/loader.c

@@ -18,11 +18,7 @@
 
 #include <kernel/thread.h>
 
-#if defined(WITH_LIB_CONSOLE)
-#include <lib/console.h>
-#else
-#error "loader app needs a console"
-#endif
+#include <lk/console_cmd.h>
 
 #if defined(SDRAM_BASE)
 #define DOWNLOAD_BASE ((void*)SDRAM_BASE)

app/loader/rules.mk

@@ -8,6 +8,7 @@ MODULE_SRCS += \
 
 MODULE_DEPS := \
     lib/cksum \
+    lib/console \
     lib/tftp  \
     lib/elf