Enabling/disabling a pull-up with a microcontroller (and a level shifter)
Enabling/disabling a strong pull-up with a microcontroller


The NPN BJT you proposed will not work. You cannot force the BJT into saturation in the configuration you have.

You could use a PNP BJT instead, but I'd suggest the best solution is to use a P-Chan FET as shown below.   







simulate this circuit &ndash; Schematic created using CircuitLab

When the Ard_GPIO signal is Low the FET is ON and the termination applied to the EMMC pin. When the Ard_GPIO pin is High the FET is OFF and the termination is floating.
There are lots of suitable P-Chan FETs but the one proposed here, the BSS84 is readily available and adequate for the purpose. If you are concerned about the RDS(on) of 17 Ohm maximum, then you could use a larger current device such as the AO3401 with extremely low RDS(on).

To simulate the circuit you need to ground the EMMC_Pullup line otherwise the simulator won't be able to do much with the signal. If the EMMC_Pullup line is left floating, then any leakage current for the BSS84 will cause the line to look high. Here is the simulation showing Vout on the BSS84 Drain and the current through the terminator resistor: