mtd: rawnand: qcom: Implement exec_op()

Implement exec_op() so we can later get rid of the legacy
interface implementation.

Co-developed-by: Sricharan Ramabadhran <quic_srichara@quicinc.com>
Signed-off-by: Sricharan Ramabadhran <quic_srichara@quicinc.com>
Signed-off-by: Md Sadre Alam <quic_mdalam@quicinc.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20230710054440.23297-1-quic_mdalam@quicinc.com