Add kcmdlinectrl to base system

Add a binary for controlling the kcmdline message for the bootloader to
the base system. The binary is similar to mtectrl, which is also listed
in this file.

Test: Verified that a custom bootloader is able to read the data
Bug: 278052745
Change-Id: I5f13a9bdff940517cb7b880815dfb8f396fc3844
Signed-off-by: Alice Ryhl <aliceryhl@google.com>