env: ti: j721e-evm: Update R5 SPL rproc env variables for J7200

The R5 SPL on J7200 SoCs will be limited to booting just the
MCU R5FSS0 R5F core in LockStep-mode at present, so add the
two required environment variables 'addr_mcur5f0_0load' and
'name_mcur5f0_0fw' that are needed by the R5 SPL early-boot
logic. The firmware name used is also different from that on
J721E SoCs.

Signed-off-by: Suman Anna <s-anna@ti.com>