radeonsi: fix array textures layer coordinate

radeonsi: fix array textures layer coordinate

Like for cube map (array) gather, we need to round to nearest on <= VI.

Fixes tests in dEQP-GLES3.functional.shaders.texture_functions.texture.*

Cc: mesa-stable@lists.freedesktop.org
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
(cherry picked from commit 87f7c7bd6566dbd95214df9b058bca5e6573374e)
[Juan A. Suarez: apply patch over si_shader.c]
Signed-off-by: Juan A. Suarez Romero <jasuarez@igalia.com>
Conflicts:
	src/gallium/drivers/radeonsi/si_shader_tgsi_mem.c