MIPS: Alchemy: devboards: consolidate files

Share some code and merge small files:
- Extract the prom init code from all devboard files (they only differ in
  memory configuration).
- Merge the irq configuration into board setup code.
- Merge smaller files into board setup code.

Signed-off-by: Manuel Lauss <mano@roarinelk.homelinux.net>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

 delete mode 100644 arch/mips/alchemy/devboards/db1x00/init.c
 delete mode 100644 arch/mips/alchemy/devboards/pb1000/init.c
 delete mode 100644 arch/mips/alchemy/devboards/pb1000/irqmap.c
 delete mode 100644 arch/mips/alchemy/devboards/pb1100/init.c
 delete mode 100644 arch/mips/alchemy/devboards/pb1100/irqmap.c
 delete mode 100644 arch/mips/alchemy/devboards/pb1200/init.c
 delete mode 100644 arch/mips/alchemy/devboards/pb1500/init.c
 delete mode 100644 arch/mips/alchemy/devboards/pb1500/irqmap.c
 delete mode 100644 arch/mips/alchemy/devboards/pb1550/init.c
 delete mode 100644 arch/mips/alchemy/devboards/pb1550/irqmap.c
 create mode 100644 arch/mips/alchemy/devboards/prom.c