fs_mgr: fs_mgr_get_boot_config_from_kernel_cmdline deal with quote

Spans quoted with " are dealt with atomically, and are stripped from
the key/value results when parsing the kernel cmdline.

Test: compile, device boot, fs_mgr_unit_test
Bug: 109821005
Change-Id: I45f3d7395f34295edefdeaafa4c15c6ee25cc4da