MFC r358176-r358177

r358176:
linuxkpi: Add list_is_first function

This function just test if the element is the first of the list.

Reviewed by: hselasky
Differential Revision: https://reviews.freebsd.org/D23766

r358177:
linuxkpi: Add str_has_prefix

This function test if the string str begins with the string pointed
at by prefix.

Reviewed by: hselasky
Differential Revision: https://reviews.freebsd.org/D23767