PCM: Major simplification of the sub-sampling design.  Now need no extra buffers because sub-sampling is done in place

NxPlayer needs to set curbyte field to zero before enqueuing a buffer.  Otherwise, it looks like beginning of the buffer has already been consumed

Change naming from cp_XYZ_cache() to arch_XYP_cache() so that all cache operations will pick up L2 support if it is enabled

 New cache.h file.  Renames cp15_XYZ_cache() to arch_XYZ_cache() and addes L2 cache support if L2 cache is enabled

 Rename ARMv7-A cache.h to cp15_cache.h.  Things will be broken on this commit until I get the new cache.h in place.

arch/arm/src/armv7-a/arm_l2cc_pl310.c, l2cc.h, l2cc_pl310.h, Kconfig:  Add initiali support for the ARM L2CC-PL310 L2 cache.

rch/arm/armv7-a/l2cc_pl310.h:  Move arch/arm/sama5/chip/sam_l2cc.h to arch/arm/armv7-a/l2cc_pl310.h.  Adjust the two corresponding Kconfig files as well.

LPC17 Ethernet: Added option to use the kernel worker thread to do most of the workload with CONFIG_NET_WORKER_THREAD option in Kconfig.  Eliminated a problem with PHY DP83848C : it doesn't need a specific initialization on mbed. Critical bufix: From time to time (after some hours) the Ethernet receiver would lose one receive interrupt and the IP stack never recover because there is no receive watchdog as the transmit watchdog.  From Max

 Correct the initial value of the BASEPRI register.  This was apparently never being initialized.  From Max