mimxrt1050_evk: Update jlink device name

A bug in the jlink application made it impossible to use OpenSDA
firmware with the mimxrt1052 device name, so we used the generic
Cortex-M7 device name as a workaround. This bug was fixed in jlink
V6.32h (2018-07-05), so now we can use the more specific device name.

Signed-off-by: Maureen Helm <maureen.helm@nxp.com>