ARM: rpc: rename RAM_SIZE macro

ARM: rpc: rename RAM_SIZE macro

The RAM_SIZE macro in mach/hardware.h conflicts with macros of
the same name in multiple drivers, leading to annoying build warnings:

In file included from drivers/net/ethernet/cirrus/cs89x0.c:79:0:
drivers/net/ethernet/cirrus/cs89x0.h:324:0: error: "RAM_SIZE" redefined [-Werror]
 #define RAM_SIZE 0x1000       /*  The card has 4k bytes or RAM */
 ^
In file included from /git/arm-soc/arch/arm/mach-rpc/include/mach/io.h:16:0,
                 from /git/arm-soc/arch/arm/include/asm/io.h:194,
                 from /git/arm-soc/include/linux/scatterlist.h:8,
                 from /git/arm-soc/include/linux/dmaengine.h:24,
                 from /git/arm-soc/include/linux/netdevice.h:38,
                 from /git/arm-soc/drivers/net/ethernet/cirrus/cs89x0.c:54:
arch/arm/mach-rpc/include/mach/hardware.h:28:0: note: this is the location of the previous definition
 #define RAM_SIZE  0x10000000

We don't use RAM_SIZE/RAM_START at all, so we could just remove
them, but it might be nice to leave them for documentation purposes,
so this renames them to RPC_RAM_SIZE/RPC_RAM_START in order to
avoid the build warnings

Signed-off-by: Arnd Bergmann <arnd@arndb.de>