macintosh: change some data types from int to bool

Change the data type of the following variables from int to bool
across all macintosh drivers:

started
slots_started
pm121_started
wf_smu_started

Some of these issues were detected with the help of Coccinelle.

Suggested-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>