Add a new feature --generate

With this argument the tool generates a Kconfig fragment with the security
hardening options for the selected microarchitecture.

Refers to #67.

This Kconfig fragment can be merged with the existing Linux kernel config:

$ ./bin/kconfig-hardened-check -g X86_64 > /tmp/fragment
$ cd ~/linux-src/
$ ./scripts/kconfig/merge_config.sh .config /tmp/fragment
Using .config as base
Merging /tmp/fragment
Value of CONFIG_BUG_ON_DATA_CORRUPTION is redefined by fragment /tmp/fragment:
Previous value: # CONFIG_BUG_ON_DATA_CORRUPTION is not set
New value: CONFIG_BUG_ON_DATA_CORRUPTION=y
...