docs: Format bit shift and hex notation for bitwise flag enums

docs: Format bit shift and hex notation for bitwise flag enums

Big number itself does not make much sense in some cases. Format the
bitshift format as well.

Changes our web page docs from:

VIR_MIGRATE_POSTCOPY = 32768 : Setting the VIR_MIGRATE_POSTCOPY...
VIR_MIGRATE_TLS      = 65536 : Setting the VIR_MIGRATE_TLS flag...

to:

VIR_MIGRATE_POSTCOPY = 32768 (0x8000; 1 << 15)  : Setting the VIR_MIGRATE_POSTCOPY...
VIR_MIGRATE_TLS      = 65536 (0x10000; 1 << 16) : Setting the VIR_MIGRATE_TLS flag...

Signed-off-by: Peter Krempa <pkrempa@redhat.com>