Add the definition for GR-LYCHEE in mbed_rtx.h
Add the definition for GR-LYCHEE in mbed_rtx.h

In mbed_rtx.h file, I added the definition for GR-LYCHEE to use the "Dynamic Heap" processing when the target is GR_LYCHEE.

betzw/mbed-os,andcor02/mbed-os,andcor02/mbed-os,c1728p9/mbed-os,kjbracey-arm/mbed,andcor02/mbed-os,andcor02/mbed-os,betzw/mbed-os,karsev/mbed-os,c1728p9/mbed-os,mbedmicro/mbed,c1728p9/mbed-os,andcor02/mbed-os,karsev/mbed-os,betzw/mbed-os,c1728p9/mbed-os,kjbracey-arm/mbed,mbedmicro/mbed,karsev/mbed-os,karsev/mbed-os,kjbracey-arm/mbed,andcor02/mbed-os,c1728p9/mbed-os,mbedmicro/mbed,karsev/mbed-os,karsev/mbed-os,mbedmicro/mbed,betzw/mbed-os,mbedmicro/mbed,betzw/mbed-os,c1728p9/mbed-os,betzw/mbed-os,kjbracey-arm/mbed