phase2+3/startcode: Add missing RTC interrupt

This adds a missing second RTC interrupt to the list of interrupt
vectors in startcode.s.

See: "K60 Sub-Family Reference Manual", K60P100M100SF2V2RM, Freescale Semiconductor, section 3.2.2.3 Interrupt channel assignments, Table 3-4. Interrupt vector assignments, on pages 75-79

Signed-off-by: Joakim Gebart <joakim@gebart.se>