mtd: rawnand: qcom: allow override of partition parser

Commit 82bfd11f ("mtd: rawnand: qcom: Add support for Qcom SMEM
parser") made qcomsmem the only parser for qcom_nandc partitions. This
might be problematic for systems with both SPI and NAND MTD devices.
When booting from SPI flash the partition table should not apply to the
NAND flash.

Prepend cmdlinepart and ofpart parsers to allow override of the
partition parser.

Cc: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/cf470f05af514acd5bd94548804ffa96b966a0a8.1619029869.git.baruch@tkos.co.il