build(corstone1000): rename diphda to corstone1000

diphda platform is now being renamed to corstone1000.
These changes are to replace all the instances and traces
of diphda  corstone1000.

Change-Id: I330f3a112d232b99b4721b6bf0236253b068dbba
Signed-off-by: Arpita S.K <Arpita.S.K@arm.com>
Signed-off-by: Vishnu Banavath <vishnu.banavath@arm.com>