tpm: select ANON_INODES for proxy driver

The newly added vtpmx driver fails to build if CONFIG_ANON_INODES
is disabled:

drivers/char/built-in.o: In function `vtpmx_fops_ioctl':
(.text+0x97f8): undefined reference to `anon_inode_getfile'

This adds a Kconfig 'select' statement to ensure it's always there
when we need it.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Fixes: 794c38e01358 ("tpm: Proxy driver for supporting multiple emulated TPMs")
Acked-by: Stefan Berger <stefanb@linux.vnet.ibm.com>
Acked-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>