Signed-off-by: Devaraj Ranganna <devaraj.ranganna@arm.com>

Use a more descriptive name (arm-corstone-platform-bsp)
for the main CMake target library provided by the project.
The older name, `target-corstone300`, did not take into
account that platforms other than Corstone-300 will
be supported in the future.

Signed-off-by: Hugues Kamba-Mpiana <hugues.kambampiana@arm.com>

Replace the generic `TARGET_PLATFORM` CMake variable
to select hardware target platform with
`ARM_CORSTONE_CMSIS_BSP_TARGET_PLATFORM` as it is
less generic and thus less likely to clash with any other
variable used by other projects.

Signed-off-by: Hugues Kamba-Mpiana <hugues.kambampiana@arm.com>

Provide more information on what the project is
all about and how to use it.

Signed-off-by: Hugues Kamba-Mpiana <hugues.kambampiana@arm.com>

Signed-off-by: Devaraj Ranganna <devaraj.ranganna@arm.com>