ASoC: img: Imagination Technologies sound should depend on MIPS

Before, all Imagination sound symbols were gated by the SND_SOC_IMG
symbol, offering the user a simple option to hide them all.  After the
removal of this gate symbol, all symbols are exposed to the user, even
when configuring a kernel for a non-Imagination platform.
Fix this by adding a dependency on MIPS, to prevent asking the user
about these drivers when configuring a kernel for a different
architecture.

Fixes: b13f7eef ("ASoC: img: Standardize ASoC menu")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://patch.msgid.link/242832f225ae68018111648ea9934dc059741567.1751989463.git.geert+renesas@glider.be


Signed-off-by: Mark Brown <broonie@kernel.org>