Set Game Default Frame Rate to 60 when sysprop not set

In previous patch, when the sysprop controlling the game
default frame rate,
"ro.surface_flinger.game_default_frame_rate_override",
is not set, it will not have any effect.

This patch sets the frame rate to 60 if
"ro.surface_flinger.game_default_frame_rate_override"
is not otherwise set to a different value.

Bug: 286084594
Test: atest GameManagerServiceTests
      atest CtsGraphicsTestCases --test-filter "SetFrameRateTest*"
      atest CtsFrameRateOverrideTestCases
Change-Id: Ia14cfa831b1418d6d2e22a77235f2ae07394a9f5