Provide alternative memory reservation from USB RAM on LPC17xx.

Provide alternative memory reservation from USB RAM on LPC17xx.

The lpc_reserve_usb_ram() serves to runtime reserve
memory in USB RAM area after linker allocated variables.
There is no mechanism to release memory allocated
by by lpc_reserve_usb_ram(). Mechanism is provided
for one time reservation at application startup.

The uLAN driver and DOGXL display drivers can
be instructed to use this kind of allocation
by inclussion of next lines in application program.

  #include <hal_machperiph.h>

  void *(* const gr_driver_reserve_ram)(size_t size) =
	lpc_reserve_usb_ram;

  void *(* const ul_drv_reserve_ram)(size_t size) =
	lpc_reserve_usb_ram;

Signed-off-by: Pavel Pisa <pisa@cmp.felk.cvut.cz>