The description of the IOMUXC_GPR2 register is wrong. It contains exactly the same description as the LDB_CTRL register. The bits in the LDB_CTRL register work as advertised opposed to the GPR2 register.
This is intentional. The LDB_CTRL description in the RM says "The register is implemented in the IOMUX Controller block (IOMUXC), as the register IOMUXC_GPR2.". And you will notice the two registers have the same address.