device-manager: Support kernels with CONFIG_VT=n

At the moment, plymouth requires VT support be enabled in the kernel
to show graphical splashes.

This is because:

1. it relies on the tty to show details
2. when VT support is disabled the kernel will use ttyS0 as the default
console which makes plymouth disable graphical splashes since it assumes
the machine is a server with a serial console.

This commit addresses the first problem by disabling the
escape-to-toggle-details feature and addresses the second problem by
introducing a new kernel parameter plymouth.graphical that is like
the "splash" option and "plymouth.ignore-serial-consoles" option
combined.