Update Imagination waiver #229

Update Imagination waiver #229

vulkan-cts-1.2.7.0 introduced new tests to validate that an
implementation clamps the most negative snorm values to -1.0 when
using linear filtering.

There is an existing waiver that covers some Imagination GPUs which do
not correctly round negative snorm values.

Update this waiver to apply to the newly added tests.

Affects
dEQP-VK.texture.conversion.snorm_clamp_linear.*

VK-GL-CTS issue: 229
VK-GL-CTS issue: 2989

Change-Id: Ic23f0a042f7489bcfd9fb838260e920f7d19f2c6