test_firmware: Use kstrtobool() instead of strtobool()

test_firmware: Use kstrtobool() instead of strtobool()

[ Upstream commit f7d85515bd21902b218370a1a6301f76e4e636ff ]

strtobool() is the same as kstrtobool().
However, the latter is more used within the kernel.

In order to remove strtobool() and slightly simplify kstrtox.h, switch to
the other function name.

While at it, include the corresponding header file (<linux/kstrtox.h>)

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Acked-by: Luis Chamberlain <mcgrof@kernel.org>
Link: https://lore.kernel.org/r/34f04735d20e0138695dd4070651bd860a36b81c.1673688120.git.christophe.jaillet@wanadoo.fr
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Stable-dep-of: 4acfe3dfde68 ("test_firmware: prevent race conditions by a correct implementation of locking")
Signed-off-by: Sasha Levin <sashal@kernel.org>