dt-bindings: imx6q-pcie: Restruct reg and reg-name

dt-bindings: imx6q-pcie: Restruct reg and reg-name

snps,dw-pcie.yaml already have reg and reg-name information, there is
no need to duplicate it here.

Add 'if' check for existing compatible string to restrict reg and reg-names,
in preparation for adding a add new compatible string with difference reg-names
sets.

Link: https://lore.kernel.org/r/20240220161924.3871774-9-Frank.Li@nxp.com
Signed-off-by: Frank Li <Frank.Li@nxp.com>
Signed-off-by: Lorenzo Pieralisi <lpieralisi@kernel.org>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Acked-by: Rob Herring <robh@kernel.org>
Acked-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>