safemode.h: Update coding style
kernel safemode: Add functions to get options early

Add get_safemode_option_early() and get_safemode_boolean_early() to get
safemode options before the kernel heap has been initialized. They use a
simplified parser.
x86: Disable PAE, if 4 GB memory limit safemode is set
boot loader: apply_boot_settings(): Replace string literal
boot loader: Always show 4 GB memory limit safemode option

On x86 we mainly want to disable PAE, which is now also used with less
memory as long as NX support is available. Ideally we'd check this
condition as well and only add the menu item, if the kernel would
enable PAE.
KDL "mapping" command: Fix argument check

It wasn't possible to actually specify the second argument (team ID).
KDL "mapping" command: Allow specifying a thread ID

... instead of only a team ID.