Add missing timer stubs to pic32mx

[btashton]

Only timer2 was stubbed out on the pic32mx. This adds the missing stubs for timers 1-5.
Prior:

❯ ./mipsel-softmmu/qemu-system-mipsel   -machine pic32mx7-explorer16   -nographic -monitor none   -serial stdio   -kernel  ~/nuttx/wrk/nuttx/nuttx.hex 
Board: Microchip Explorer16
Processor: M4K
RAM size: 128 kbytes
Load file: '/home/bashton/nuttx/wrk/nuttx/nuttx.hex', 250268 bytes
nx_start: Entry

After:

❯ ./mipsel-softmmu/qemu-system-mipsel   -machine pic32mx7-explorer16   -nographic -monitor none   -serial stdio   -kernel  ~/nuttx/wrk/nuttx/nuttx.hex 
Board: Microchip Explorer16
Processor: M4K
RAM size: 128 kbytes
Load file: '/home/bashton/nuttx/wrk/nuttx/nuttx.hex', 250268 bytes
nx_start: Entry
uart_register: Registering /dev/console
uart_register: Registering /dev/ttyS0
uart_register: Registering /dev/ttyS1
nx_start_application: Starting init thread

: ttShell (NnxSH) NuttX_sta-1rt0.0.1
nsh> CPU0: Beginning Idle Loop