sifive_u: Rename memmap enum constants

Some of the enum constant names conflict with the QOM type check
macros (SIFIVE_U_OTP, SIFIVE_U_PRCI).  This needs to be addressed
to allow us to transform the QOM type check macros into functions
generated by OBJECT_DECLARE_TYPE().

Rename all the constants to SIFIVE_U_DEV_*, to avoid conflicts.

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-Id: <20200911173447.165713-3-ehabkost@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>