It is strange to short lines together when you have already taken the effort of routing them on the PCB.
My guess is that the tracks are actually routed to the MX31L, probably with a pull up to a voltage rail. My guess also is that the pull-up voltage is connected to a disabled regulator
Internally, the MX31L can route the SDIO interface to different GPIO pins, and in addition to this you need to configure how the pin is internally driven (internal pull-up, internal pull-down, ground or open-drain)
The external pull-ups are neccesary nevertheless, mainly to avoid glitches in the power-up procedure before GPIO configuration.
So summarising this is my take:
- The SD card lines are connected to the MX31L. In the worst case, they have DNP 0 ohm registors on the lines... check if they are 5 unpopulated registors near the MX31 IC.
- There are 5 pull up registors to a power rail. My belief is that there is a footprint for a regulator, but they have not placed it. I do not believe it is SW disabled because that may induce some standby current leakage. Look for an unpopulated IC.
- We need to identify the pins connected to the lines, this can be tedious, but with patience can be done with some kernel programming and colorful leds.
- Once that is done, then we need to create a kernel module to change the GPIO. I believe the MX31 SDIO mxc driver will do nicely.
Warning, there may be a very good reason the SD card is not enabled.
The MX31L has up to three SDIO interfaces, but the number of external pins is limited, so on production the integrator can choose to make one available. This is called pin sharing or pin functionality multiplexing...
Unfortunately the 3G modem may be connected using SPI/SDIO interface (other option will be USB, or UART but that will be strange...). On the worst case the unpopulated SDcard and the 3G module may be sharing resources, so in the future we may have a SD card, but enabling it will disable 3G network.
Also because of this... if you play with the SD module... Remove the 3G module!!!