Remove the 'epit' variable from the generic imx31 and imx53 specification,
and only add it to base-hw specific i.MX specs. Thereby the EPIT timer
library gets build for base-hw only.
Moreover, fix some const-ness issues in the platform_timer implementation
for the EPIT timer.
Fixes#688.
Implies support for the ARMv6 architecture through 'base-hw'.
Get rid of 'base/include/drivers' expect of 'base/include/drivers/uart'.
Merge with the support for trustzone on VEA9X4 that came from
Stefan Kalkowski.
Leave board drivers in 'base/include/platform'.
Rework structure of the other drivers that were moved to
'base_hw/src/core' and those that came with the trustzone support.
Beautify further stuff in 'base_hw'.
Test 'nested_init' with 'hw_imx31' (hardware) and 'hw_panda_a2' (hardware),
'demo' and 'signal' with 'hw_pbxa9' (qemu) and 'hw_vea9x4'
(hardware, no trustzone), and 'vmm' with 'hw_vea9x4'
(hardware, with trustzone).
