bsps: Delete bspreset_fatal.c

Use bspreset_loop.c instead.  This avoids infinite recursion.
bsps/powerpc: Delete clock_4xx.c
bsps/powerpc: Add PPC405 support for shared clock
bsp/virtex: Rename file dlentry.S in start.S

Use default bsp_specs file.
bsp/virtex: Replace low-level BSP start code

Use linkcmds.base.  Use EABI with small-data area.
bsp/virtex: Delete unused variables
bsp/virtex: Delete bsp_XAssertHandler()
bsp/virtex: Fix warnings
bsp/virtex: Do not use PPC403 TTY driver
bsp/virtex: Move timer config to new file
bsp/virtex: Fix header includes
bsp/virtex: Use generic interrupt support
bsp/virtex: Delete BSP_ask_for_reset and BSP_panic
bsp/virtex: Remove unused configure macros
bsp/virtex: Use XPAR_INTC_SINGLE_BASEADDR

This define is also present in newer "xparameters.h".
bsp/virtex: Fix warnings
bsp/virtex: Add console devices only if present
bsp/virtex: Use shared clock driver