dt-bindings: sram: qcom,imem: Document MSM8226

Add compatible for MSM8226 IMEM.

Signed-off-by: Matti Lehtimäki <matti.lehtimaki@gmail.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20230520121933.15533-2-matti.lehtimaki@gmail.com