kmem_alloc(), kmem_free() undeclared.

[bch <brad.harder%gmail.com@localhost>]

/usr/src/sys/dev/usb/usb_subr.c:176:2: error: implicit declaration of
function 'kmem_alloc' [-Werror=implicit-function-declaration]
  char *b = kmem_alloc(USB_MAX_ENCODED_STRING_LEN, KM_SLEEP);
  ^
/usr/src/sys/dev/usb/usb_subr.c:176:51: error: 'KM_SLEEP' undeclared
(first use in this function)
  char *b = kmem_alloc(USB_MAX_ENCODED_STRING_LEN, KM_SLEEP);
                                                   ^
/usr/src/sys/dev/usb/usb_subr.c:176:51: note: each undeclared
identifier is reported only once for each function it appears in
/usr/src/sys/dev/usb/usb_subr.c:180:4: error: implicit declaration of
function 'kmem_free' [-Werror=implicit-function-declaration]
    kmem_free(b, USB_MAX_ENCODED_STRING_LEN);
    ^