[tosa] improved legalization for leaky_relu
This change (from compare+select operations, to a min/max operation) can improve implementation speed and size on some hardware platforms.
Using max/min instead of select. This change (from compare+select operations, to a min/max operation) can improve implementation speed and size on some hardware platforms.

Signed-off-by: Tai Ly <tai.ly@arm.com>
Change-Id: I6e3929873ea2b1f12fe635b4e953c14ed5bdf526